I'll be in Bangkok for 3 days (and only Bangkok). I haven't been able to find any guided tours for rock climbing in Thailand that are based in Bangkok. I've only been able to find indoor climbing in Bangkok. I'm not specifically looking for outdoor climbing in Bangkok, but a guided tour that would depart from Bangkok and head out for a day or two, and then go back to Bangkok. Do such companies exist?
Yes, companies exist (or, at least, existed recently) which provide guided outdoor rock climbing trips departing from Bangkok.
Two examples from a May 7, 2014, post on expatlifeinthailand.com (cached here):
Bouldering just outside Bangkok with Proclimber Thailand
A small purist bouldering club with a very small (and hot) wall hidden in the backstreets of Watthapra. In the dry season they have weekend trips to some great bouldering just outside Bangkok. Information can be found on their Facebook page.
A bouldering forum focused purely on the great outdoor bouldering options of Thailand, with trip to central and northeast Thailand. Just outside Bangkok near Pak Chong there are amazing bouldering options. Visit their Facebook page for more information