There is no single database for pepakura, though pep' main website DOES let users submit their designs for others to download:
http://www.tamasoft.co.jp/pepakura-en/gallery/list.php
http://www.tamasoft.co.jp/pepakura/gallery/list.php
As for activity, yes, this is not a very active thread. It's because of two reasons. It takes a lot of time and effort to make a pepakura model, and pep modeling is such a specific and small field of skill that what few pep modelers there are, usually are only working on things for themselves or things with a lot of demand. The other reason is that this is a Halo armoring website, and nearly ALL of the requests coming in lately are for non-Halo stuff. If anyone has pep requests for halo, we'll be all over that and answer it in a second, but things like power ranger sequels, npcs from A/B-list video games, and old cartoons will PROBABLY (but not deinitely) not have pep files out there, since someone needs to take the 5-odd hours to model and pep each one. If there was a bustling site for armoring these things, I am sure there'd be pep files for them, but as it stands, most people prefer to just free-ball build these things because of the lack of availability of existing material, and because foam armoring is very easy to work with even without a pep file.
I check this thread every day, and if someone asks for something I have, I'll readily supply it inthread or in a PM, but there are not that many pep files out there overall. My suggestion is that, if you really want to pep something, you should try your own hand at it! Get a fre 3d modeling program and mess around with it. I've been doing that to fill in some of the gaps in the Halo pep DB myself, and it's not that hard to do once you get the hang of it. Good luck to you all.