You could try the Pentax and Third Party Lens databases here in the forums to start.
There's
Welcome to Bojidar Dimitrov's Pentax K-Mount Page , but I think he only covers Pentax lenses, not third parties.
You could try
M42 is a site dedicated to M42 adaptator lenses. You will find here tests, from argentic to numeric cameras and oldest to newest M42 lenses. Members described their work and the used lens. Oldies, but goldies! if you wanted to use screwmount M42 lenses instead of K Mount lenses, but you'll need a good adapter to do it (will run $25-$40 or so for a good one)
I'm not sure what you mean by "digital compatible" though...all K Mount and m42 screwmount lenses are useable on Pentax digital cameras, the only concern I've heard of is that some of the newer digital specific (DA) lenses might not cover the whole frame on a full-frame digital or film camera.