Post it out in General - list your limiting criteria (materials, size, grind complexity etc) -
There is more traffic out in the General forum.
You might even cross post it a little - post the contest up on instagram and your facebook pages.
You can keep the voting/judging here even if people from those other venues choose to enter. That would even drive some traffic here to BF, since people on insta-face-twit-gram are already online.
Additionally, I really like Brad's idea regarding limiting the judging to either knife-makers or mods here on BF.
Doing those things might help come up with a design that sells, which is the point. Even if a design does not win, as the Bluegill shows, it could become a seller.
best
mqqn