Where can I find old maps of Pyeongtaek, or even southern Gyeonggi-do (1800-1990)? Are there any websites that provide camping areas or information for all of Gyeonggi-do? Any help is appreciated!
Tricky one here. My source for old Korean pictures varies greatly and there is no set site that I go to. However, I would suggest taking a look at Gusts Of Popular Feeling though. If you click here you can see a few of his photo history's on the Joseon Era. You could also take a look at his Post 1945 Era and Colonial Era pictorials as well. In fact if I were you, I would suggest sending him an email and asking him through his comment section what his source is and maybe he (Matt) could point you in a sound direction. Perhaps stopping by the ROKDrop would yield some good info as well. As I said in the intro, sometimes I don't know the best answer and I know that these guys do.
Of course, you can always spend hours on Flickr and Google, but that's not too reliable.
I can help with the website though. First, take a look at the Gyeonggi-do website and get better acquainted with the whole area. As far as camping goes, you should look at the "Natural Wonders" section found on the "Tourism" page and read through each profile. I ran through the list and saw a handful that offered camping or some sort of mountain lodging. The best way to do it would be find the location you want to go, and then do some detailed research about how to get there and what they offer at each destination.
If anybody has any questions, just send me an email at firstname.lastname@example.org or leave a comment.