Joe, check out this faq on freon alternatives:
http://www.vettenet.org/acfaq.txt
The isobutane I purchased in a red can of camping fuel. I don't remember the brand, its well known, but I think it is something like 80% isobutane and 20% propane. The top of the can is almost identical to a old R12 can, so I used a standard top clipping R12 manifold adapter. The propane was a little trickier. I had to figure out a way to attach a R12 hose onto the torch end. I removed the flame tip off the torch adapter, drilled out a small hole through pin hole sized hole at the penis like tip, rethreaded the end so a standard R12 hose adapter would screw on, and just shot it into the AC system. If you want to, you could also remove the little check valve at the base of the torch, and drill it out. I didn't premix in an external container, though that's probably more accurate. I think it was Thomas Owen who also did the same on a couple of his cars and got excellent results. You might want to check the high side pressure after you are done, because it is easy to overfill the system. Just remember that you only need to fill less than half the weight of propane as you would freon. Something like 14 oz total is sufficient for the whole system.