If you can make a reasonably close sketch, any jeweler worth their salt can turn it into a cast piece. You bring in a drawing and they'll CAD it, then you iterate. Very simple. You don't need to find anyone, because that's part of the service that many custom jewelers already offer.
I'll take a swing at it. My drawings may approximate that of Koko the gorilla (Who had better composition) but I can certainly try. I don't think that what I want is too complicated, except for the fact that I want the engagement ring and wedding band to interlock. I can't have been the first person to think of that. Neither of us are much into jewelry really, so they will likely be for ceremonial/dress purposes only. The idea of getting a band tattooed on has merit I think.