JS_Harris - 5:47 am on Apr 8, 2010 (gmt 0)
tadden, assuming you don't have duplicate content issues or title/description issues your pages don't have enough PR flowing to them to rank them all.
The fix is to ensure PR, both internal and incoming, is able to easily reach the pages you want indexed. How many clicks away is the hardest to reach page on your site?
Also, there aren't 12,000 costume related keywords that will drive significant traffic, you may want to focus on making the important pages more prominent. Good luck!