here is another list of lens mounts, but honestly, I don't this will help you that much.
Alphabetical List of Camera Mounts
for the Q, you can adapt many, many different brands of lenses. a quick search on ebay or B+H photo for "Pentax q adapter" will show you the possibilities.
do not expect that any of the automatic functions on adapted lenses will work on the Q - adapted lenses will be completely manual. luckily, the Q has focus peaking to help focus manual lenses (you can read up on focus peaking here on the forum or in your Q manual). regarding the Sigma you mention above - there would be little use in buying an auto focus lens only to use on the Q since you will not be able to use those automatic functions. but if it's really cheap, then it doesn't really matter...
I would recommend that you purchase a cheap manual focus lens (with a manual aperture ring) and a cheap adapter at first. the genuine Pentax K to Q adapter is vastly superior to the cheap chinese-made adapters, but it is also much more expensive. best to try it out on the cheap first until you have a good idea of what the adapted lenses can do for your images. if you're shooting the moon, best to look for an adapter with a tripod mount built in - you'll need it!
stick to the more common mounts - Pentax K or M42 (pentax's early screw mount), Nikon F, Canon ES, EOS or FD (their manual focus mount), Leica M or M39 (their early screw mount), Minolta MD, Olympus OM.
hope this helps.