All the obviously easy to find websites get DMCA from Nintendo. That company is notorious for going after anything Pokemon that doesn't give them a copyright royalty payment.
I have seen very broken sets of pictures on some image sites, but they were just small batches of pictures that particular uploader likes.
You'll have to find hoarding collectors out there among the Pokemon fans. They are the ones to keep private FTP and other servers going where games, mods, image collections, and artbooks are collected. Your other alternative for easily available online sites is to find Pokemon artbooks that show off the pokemon cards. BakaBT is a torrent site with many artbooks, so look them up.
SFW Pokemon Artbooks
https://e-hentai.org/?f_cats=767&f_search=artbook+pokemon 
