You can get the Liquitex at Hobby Lobby or any painting supply store. I use the 70% alcohol for thinning. My ratio is something like this:
60% paint - 30% alcohol- 10% retardent
Keep in mind. You don't always have to use retardent. The only time I use it is when I will have the AB in use for a while with a complicated paint scheme or freehanding something. If you are just laying down primers or single finish coats, just thinning with alcohol should do you.
Andy