Write a somewhat longer ad on Craigslist. Explain the job first, then explain that your company is in the adult field and they will be working with explicit materials (if they will) but that your office environment is as professional as any other.

We were having problems like you're describing, but once we described clearly what the job was and that we were a real business, we ended up getting some great applicants (and a few with screws loose, but that's another story...)