Adderall would probably be the easiest to find being your best option. Dexedrine might be better since it's less harsh on the body and less side effects. Cocaine shouldn't give you unmanageable withdraws to start with. You are just going to end up getting hooked on amphetamines.
Ritalin is said to be very similar to cocaine, but I don't think that it would really be safer. A lot of the pills are XR and have some nasty fillers/binders. That's not to say that the coke doesn't have a bad cut, but I don't see much of a benefit unless you were to take the Ritalin orally.
Umm idk about you but I would use a downer like xanax or klonopin for the come down, if you time it right, ie eat your xanax as your doing the last 15 min worth or so of coke, you will feel virtually no comedown. I don't use coke w/o heroin, or by itself with a benzo for the comedown..
Adderall or Dexedrine for a coke substitute, although amphetamines and cocaine are different drugs of course. Ritalin is very weak IMO, I was prescribed to it for a little while before being switched to Dexedrine..