Not sure about when or if it will be banned but AX has stopped production on PP so it will only be around for a short time longer. Look around at some supplement web sites and you will find some.
As far as stacking, you're right, most either take it stand alone or stack with superdrol such as the following:
Week 1: PP 20mg
Week 2: PP 30mg
Week 3: PP 20mg/superdrol 10mg
Week 4: SD 20mg
Week 5: SD 20mg
There are variations but you should run SD no longer than 3 weeks because the compound wreaks havoc on your lipids and gains drop off after the first three weeks anyways.
Remember to do a good post cycle therapy and take some time off between cycles. Bloodwork before and after is also recommended. Be safe.