I agree with Don. You need to plan your marketing outside of the playing card community. I call this a "dual community concept." The big win will come from marketing to those who are interested in Greek mythology, history, and literature.
I don't want to say the playing card community is low hanging fruit but it has a better awareness of playing card projects. You still need to market the playing card community but increase your effort outside of the community and in the concept community (i.e., message boards, Facebook groups, partner with blogs or websites, etc.).