What have you done so far? As a climber/boulder-er myself, I think climbers can be qualified as an affinity group. In other words if you can get a few climbers using the site (and they like it) they should pass the info about your site to other climbers. Or think of how most climbers use the internet - what sites do they use - that's another source of marketing ideas (think cross promotions). Have you tried to post information about your site on relevant blog/forum sites?
