Years ago (20-plus), I worked for a large publisher of trade magazines. They published such titles as Supermarket News, International Contact Lens Clinic, Metalworking News, and (as the result of an acquisition) Hog Farm Digest.
I hated giving my business card to people.
www.farmshow.com is entirely about funky home-made machines farmers build to solve problems on their farms.
www.sheepmagazine.com publishes *Sheep! *. It’s about, well, raising sheep, mostly for the small farmer in the US.
The medical and professional journals are pretty specialized.
Advances in Enzyme Regulation
Eating Behaviors
Pump Industry Analyst
Journal of Aerosol Science
Wildland Firefighter
Plus, there’s Spectacle, a Quarterly Journal of the Circus Arts. IF YOU ARE A CIRCUS PROFESSIONAL, SPECTACLE WILL KEEP YOU INFORMED!
My husband and I subscribe to Backyard Poultry Magazine. We love it.
In my days in publishing I have worked for, not just seen, all of these publications:
Democratizatsiya - The Journal of Russian Democratization
Energy Customer Management
Military Information Technology
Public Utilities Reports
Lodging Law
Lodging Technology News
Natural Gas Intelligence
Daily Gas Price Index
Weatherwise
The Journal of Group Pyschotherapy, Psychodrama and Sociometry
The Journal of Popular Film & Television
Romance Quarterly
The Journal of Genetic Psychology
And more. Few of the above ever had a readership above 1000. In the case of a few of them it was below 100.
There are, literally, hundreds of thousands of specialty magazines out there with teeny, tiny readerships on incredibly focused topics.
I remember years ago in a magazine that listed trade magazines (yes, really), being quite amused to come across The Embalmer.
The official publication of the British Institute of Embalmers.
My grandfather was in advertising and was comped subscriptions to countless magazines. Alas he’s been gone a long time. The only ones I remember now are Chain Saw Age and Rotary Screw Tractor Monthly. Those were the family favorites.
For my work I currently read Picture Framing Magazine, Decor which serves framers and the art market, Art Business News, Scrapbook Retailer*, and CNA (Craft & Needlework Age).
*I don’t retail scrapbooks or anything related to them, but our trade associations are connected. The Freeze Dried Floral Association is also under the same umbrella. Alas, I don’t get their magazine (if they have one).
I didn’t realise knitting magazines were considered “specialty”, especially when you consider how trendy knitting has become in the past few years… there are actually dozens of them out there on the market.
I’ve got a couple of copies of “Knit.1” kicking around in my craft room at the moment. The patterns tend to be designed for younger, hipper knitters (they’re definitely not your grandma’s patterns). I also routinely pick up copies of Interweave Crochet if one of the patterns catches my fancy.
I actually read an article in Supermarket News about two weeks ago. I have no life 
We used to get a magazine about batteries. All batteries, all the time. Thankfully, Readers’ Guide dropped it and so we could too.
I’ve actually written for GCN and one of my dearest friends is Senior Editor for the test lab there.
But I’d hate to call it obscure. It’s big and does a LOT of business.
Well, if girly/outright weird stuff is to be considered, how about Girls and Corpses Magazine?
No, I’m not kidding and not a subscriber.
I don’t know if I’m more surprised to see this magazine still exisits or that there’s actually a website: http://www.indianaprairiefarmer.com/
(My grandfather was actually on the cover once - in an overhead shot of a cattle auction.)
Get a load of today’s big story: “How much does your combine weigh?”
My wife is the office manager for a casket company. Her boss gets Mortuary Management and Funeral Service Insider.
There’s a handful of magazines about knife collecting.
When I had an antique Buick, I got a mag from the Buick Club of America. Surely other brands have the same. There are clubs for Mustangs and Thunderbirds, but Cougar magazine might not be about cars. 
I subscribe to QST.
Batesville?
Almost every magazine we get, I can read it and get the idea of what they’re talking about, even if I don’t know anything about the subject… except QST.
Pretty interesting magazine! I’ll bookmark it.
http://www.owlpages.com/index.php Probably the biggest compendium of esoteric owl information anywhere.