Here's a list of helpful links I've found while researching Pentax K lenses roughly organized by topic.
Some of these pages may be broken or in your non-native language. If they're broken, I'd recommend searching for them on the Internet Archive's Wayback Machine. If you need a web page to be translated, I've found Google Translate to be a serviceable solution.
If you have any links you think should be here, feel free to email them to me. The contact email address is this website's name at gmail dot com. (This hint is an effort to minimize spam)