A lot of tattoists are their own great artist. This being said, I know that some places do purchase artwork. If it were me I’d just call them and found out if they would purchase designs or not.

Or if you are really into Tattoos look into getting an apprenticeship and become one yourself

Forget it. Those guys are all good artists, too; that’s why they got in the business. But you could have them tattoo you with the designs you have created. Or you could design a line of tee shirts incorporating the designs. Or advertise to illustrate children’s stories, or otherwise become a commercial artist. Hook up with writers of fantasy stories or the designers of fantasy games and produce a lavishly illustrated book. Hook up with an auto detailer, and paint the designs on panel trucks.

Lots of good things to do with creative graphic art, but you will have to do the work yourself, not simply sell the designs to someone who already has a great many designs.