While there are plenty of online pharmacies willing to sell prescription drugs without a prescription, very few are actually effective at CTBing on. Best I've found were a few sites selling Phenobarbital, but only like 30mg per tablet, and the minimum/recommended amount to CTB on is about 10g, and that will get insanely expensive. There's a brand of Pheno that actually contains a great amount of Pheno called Barbital-100, it has 100 tablets each containing 100mg so that's 10g total. You'd only need 2 boxes just to be on the safe side for an almost guaranteed CTB. However, I've never found any clear net pharmacies that sell Barbital-100, I've only ever come across it from a single vendor who's on 2 different dark net markets.