..the best I've found are at "Penis Depot"...good price...excellent quality, quick shipping...just take your measurements very carefully for the shaft part of the cylinder otherwise if it's too short you wind up getting part of your shaft in the head cylinder part which then gives you a big donut! I had to use part of an old cylinder and attach it to the original one.
But they give great results and the head keeps the enlargement

PM me if you need more info or pics