I can't remeber the website but any A/C site should link you to a place to buy it.
I did the conversion on my 92 Civic, I took the A/C system out of a roll over, installed it on mine, had it evacuated and pressure tested at a shop. Then did the 134 coversion at home. The system would almost stall the car when I was shifting (stick)- something about a high pressure cutoff switch that should be installed when you do the conversion, I haven't looked into it much, I just let out some pressure.
When my kids same year Civic with A/C finally died I tried to compare the wiring harnesses to see if it was converted. His had a grey plastic piece of plastic wrapped with blue elctrical tape and two wires coming out of it near the fan relays, mine did not. I couldn't figure out if it was a factory piece or a converted piece, the wires to and from it were way different than mine. It's been two years and still works pretty good. Although in Buffalo I only use it when really hot and that's not very often.
So you have three options now: find some r12 and pay , find freeze 12 (r 12 compatable,add and pray or convert to 134 and pray.