This is the product I use to flush AC systems. http://www.amazon.com/FJC-Flush-Solvent-1-Quart/dp/B000HTNPLU
Alcohol, laquer thinner, or mineral spirits won’t remove or neutralize any acids that may be in the AC system. And you don’t want to use anything that may leave a residue in the AC system.
You can still get R12 refrigerant. But you have to be licensed to purchase it, and it ain’t cheap.
Tester