I always thought the back of Trail was the place to look for such ads, but I haven't read it for years.
Try phoning up companies directly - even if they don't have positions vacant, they might know someone who has.
For what it's worth, there were a couple of jobs going in Snowdonia this year for outdoor activity co-ordinators. Pay is pretty poor though - less than £14k. Could you live with half your pay?
The other thing to consider is your qualifications - having SML, SPA and canoeing/sailing trainer-level awards is an immense help, as (of course) is plain old Experience.