If you type "Pentax Lens Reviews" into a search engine you should come across a site with "Pentax" in the address which has a huge database of lenses and reviews of same. Don't just go by the number score as this can be skewed by people who had a bad example or (in one egregious example I found) stated that they only give top marks to lenses with "Ltd" on and therefore wouldn't give the one being reviewed a high score!

There's also the Bojidar Dimitrov K mount site - he has built a listing of pretty much everything related to K mount Pentax cameras including flashes, winders, etc. Useful for seeing what was made and therefore what to look for.