No clue where this went but here's my experience. There's a huge demand for industrial equipment repair in addition to machine tools. This might be slightly easier to break into than heavy equipment repair.
I worked for a shop with hydraulics and punematics in the title. The fact was we'd work on just about anything. The bread and butter was 15-60HP rotary screw and 5-15HP piston air compressors which lead to a lot of other work of by the way while you are here can you look at this as well. We worked on compressors everywhere but lots of car dealerships & repair shops, a national tire chain, and a fair amount of factories.
He had service agreements set up with most customers where we'd service their compressors every 3-6 months which was enough in it's self to keep 2-3 guys busy. While we were servicing a compressor if something was broken we usually had the parts on the truck to fix most basic things and run their backup system to insure it would work when they needed it. Compressors are usually kept in a corner and get 0 attention till they stop working but when they do they cripple a business. A lot of times we'd show up for a broken compressor and then get them agree to letting us service their compressor to prevent down time. He had 1-2 diesel compressor on hand for emergencies and then some rental machines as well to save the day. He could usually have someone there pretty quick when a shop was down. it was amazing the amount of shops who did 0 maintenance before something broke and we started servicing their equipment. I'm guessing if you stopped by 200 shops with air compressors you'd have a decent amount of work.
We then worked through miner fixing things like loading docks, cardboard balers, and clothes carousels in the back of big box stores they are a middle man between big box stores and contractors, I think there's several other companies out there that do the same thing.
We also worked on things like diesel compressors, tree trucks, all the equipment at a plant that made plastic ponds, rebuilt hydraulic cylinders for a bunch of heavy equipment, car lifts and other automotive shop equipment, and were the people to call when the OEM didn't want to support old obsolete junk. Most of our work was word of mouth though he did have a basic website but it doesn't come up on the first page when searching air compressor repair Denver.