I’m looking for advice here on how to go about buying a loose gemstone / fitting to assemble a ring. Googling where to purchase a gemstone gives plenty of hits, but the sites seem to be iffy, at best (as well as located outside the US). If websites are definitely the shadier way to go, do standard jewelers sell loose gemstones alongside already finished items? Neither myself nor any of my friends are very much into jewelry, so none of us know the answers to these questions. Help is much appreciated, and thankfully the target of this gift doesn’t read message boards 
Umm… if you’re not into jewellery, why are you trying to assemble it yourself. Just go to your local jeweller.
My advice is to go to a large local gem show. At the show you will find multiple vendors, and you may find a few who will be willing to educate you. Ask to see lots of stones and ask lots of questions. Many gem vendors are in the business out of love, and like many amateurs, are only too willing to share their passion with you.
Pricescope.com’s forums are very hospitable to newbies—I’ve asked a few questions on them and have been pleased with the content and tone of the responses. I would browse the threads there, and perhaps ask their multitude the same question you’ve asked here.
As to why you would want to buy loose gems, if your taste is esoteric, you may not be able to find the gem + setting at your local jeweler. A good local jeweler should be able to assemble the piece for you. Alternately, the loose gem vendor will know of multiple sources for settings and jewelers.
Good luck.
Blue Nile is a reputable online gemstone dealer.
I’m not sure how large of a stone you are looking to get. But you definitely should pick your large center stone first and then decide what design you like and what complimentary stones you want around it.
The keys to picking diamonds are the four C’s.
Cut, Clarity, Color and Carats. Each of these characteristics will effect the price of your stone. And there are trade-offs that you can make, to save you money. Not every flaw in a diamond is visible to the naked eye, yet, these minor flaws, can significantly reduce the price of the stone.
In addition, you will need to know what shape of the diamond you want (round, oval, pear, etc.)
I would also recommend that you get a certification of the stone and then have it appraised for insurance purposes. And do get it insured. Depending upon the cost of the stone, it may not be covered under your homeowners or renters policy and you will need a separate insurance rider to cover it. Rings do get lost or stolen.
While there is a tendency to want to do all of this to surprise your special some-one. I would encourage you to include her in the discussion, especially about shape and design of the ring. Assuming this is an engagement ring your talking about, this is something she will be wearing for a long time (hopefully) and you want to make sure she likes it.
Good luck.
See, this is how little we know 
I wasn’t sure that local jewellers would do this for you. I’ll be heading into the city to ask around then.
If “the city” for you means New York City, then head over to the “Diamond District” on West 47th St. between 5th and 6th Avenues. I got my wife’ engagement ring there assembled from loose stones chosen at two different places (diamond from one, pair of sapphires from another) and the ring/setting from yet another place. They have drawers of stones sorted by color and size.
If a given place isn’t in the “finding and setting a loose stone into your existing ring” business they will point you to someone who is.
When we were looking for my engagement ring, we called our insurance agent and asked what local jeweler he recommended for appraisals and replacement work. Turned out to be a great relationship.
I’d recommend Pricescope as well - if you are after coloured stones the forum there is great for recommendations to precision cutters like Jeff White and Gary Braun (both Gemmy winners and based in the US).
Try:
[url=]Firemountaingems
You can find both mountings and gemstones at each site. I order from them a lot and have always been satisfied.
It takes a little practice to mount gems into the settings; try starting out with larger sizes. Many of the semi-precious stones (citrine, amethyst etc.) are reasonably priced. These would not be ultra high quality-flawlessly cut stones that are best kept in a safety deposit box, but they’re fine for when you want something a little better than costume.
http://www.riogrande.com/ , off the top of my head. They’re reliable.
About a month ago, we bought a loose 1/2 carat diamond from James Allen. They had very good prices, a wide selection and delivered very quickly. They’re A+ rated by the BBB.
Go to pricescope.com and ask there. I bought my loose diamond from goodoldgold.com. Pricescope is a consumer advocacy site for diamonds/ gems.
Revisiting this thread to say thank you, all! I wound up going to a jeweler about 90 mins away, when my excuse was to help my friend fix up his basement. Found something there, proposed in April, and will be putting our deposit down tonight for our wedding
Congratulations!
Find the Gem Shopping Network on your cable network. They offer some great deals and 90% of the hosts are long time antique dealers and are selling jewelry from their own personal collections. They sell alot of top quality gem stones that you can’t find in stores and also estate pieces.
Reported.
??? What are you reporting, on a thread where the most recent post was made in July of 2011?
Removed spammer.
ETA: the mods forgot to remove the “reported” post. The spammer may have hit several threads and had those posts removed en masse.