Are centrophenoxine and choline bitartrate also available on those sites? Do you buy them by themselves? And how much do you take?

Any site that sells aniracetam will sell at least choline bitartrate. You usually buy them by themselves. I get mine in powder form and create the capsules myself. I create capsules with a controlled ratio of piracetam, aniracetam and centrophnisine then vary how many I take and how often as appropriate.

If taking just ani and centro a suitable, fairly conservative dose would be 500mg Ani + 250mg centro twice daily.

Not that with racetams the full effect can be expected after about two weeks.