You have to find your own paste. Power diplomacy to 400 it dead easy. Just do lockbox missions. You may even come out ahead.
See now there's the problem with Biochem. You have to find your own paste because it sells raw for more than it sells when made into a stim.
There really isn't good money to be made with Biochem any more. You'll make more selling the raw materials than you will the finished goods.