I’ve played Blue Steel for about 40 years. Now I need to switch to a lighter gauge and the .009-.042 Light set is apparently out of stock everywhere. What is anyone’s favorite brand/make?
Am I mistaken in thinking I see the ones you want, in stock on Amazon?
There, but expensive. When I buy from Musician’s Friend I buy 10 sets and get them for $4 per or so.
And besides, I’d like to hear what other strings folks use/recommend.
That’s a good idea. I don’t play guitar so I was clueless on prices.
Check out the cost of buying bulk (a dozen of one gauge string). You can have any gauge you want then. It’s likely that if you break strings it tends to be the same string(s), at least it was that way for me. So I gave up buying sets. Plus I like and need a very light set. 12 strings cost between 4 and 10 dollars depending on gauge. You might be able to get the equivalent of 12 sets for $40 or so.
I used to use Blue Steel but at some point I switched to DR. I wanted to try flatwound strings and ended up liking them better. The flatwounds are much more expensive, but they last longer, theoretically. A lot of people don’t care for the duller tone of flatwound strings but I like it.
Sometimes “duller” just means stronger on the main note and lighter on the harmonics. You can call the ones with stronger harmonics “brighter and more alive”, or you can call them “jangly and irritating”. Depends on the way you like to play.
I like bright and jangly. 
I usually just get Slinky’s.
I LOVE the sound of new strings.
I’m assuming acoustic here but your best bet is to try a few out for your guitar. I’m partial to D,Addario EXP 16 s for my Taylor and Garrison and Martin Sp Lifespans or D’Addario coated strings lights for my Seagull and Goya 12 strings. I usually get mine at juststrings.com or stringsandbeyond.com. both offer great service and prices.
Good Luck in your hunt!
Martin silk and steel are nice.
If you know exactly what you want, and you know you’re going to stick with them, that sounds great.