tracking down a leak

If you have a way of evacuating the system AFTER you stick a foreign material in there, pressure testing is a legit method, but I would NOT use air (water vapor in air)

You have a welder? Co2/ Argon bottle? Nitrogen? You can pressurize with that, but I'd start with 30--50 lbs, and if that does not show up, don't be afraid to go up to 2-300 psi. After all the normal condenser operating pressure is "up there."

But if you don't have a vacuum pump, don't have a way of measuring a new charge, or proper instrumentation to recharge the thing, I'd stick with dye or even as suggested, a "sniffer"

Your "top suspects" are more like to be compressor seal and the high pressure end of the system, but it actually can be anywhere, and not just the fittings, either. Pinhole in a hose, a tube, or the coils. Use a lamp and small mirror to look around stuff, the rear of the evap, if you can get there, and the compressor.

I'm as bad off as you. I've got many pounds of R12, 22, and even some 502 from my HVAC/R days, and the only R-134 I've got is a few cans I bought. If I'd known it was gonna skyrocket, I"d a bought a few more!!!