I posted a guide to introduce people on
how to edit the database for Paragon Chat to use NPC/Villain costume parts.
While it isn't an encyclopedia of parts to choose from, if you are okay with doing the above, that's 50% of the battle. Finding the parts is the other 50%.
The simplest to say advice (not necessarily the easiest or fastest method) is to use Icon in NPC mode, put the Mender parts on a toon (this might take some time) and use Demorecord commands to save the costume to a text file (Icon and Demorecord are both documented on Paragon Wiki), then use a database editor to punch in the parts to a costume you have (that last part the guide above can explain).
Bear in mind, NOT ALL NPC PARTS will validate in Paragon Chat as a working player costume. It took some trial and error by the community to get Crab Spiders back with their leggy backpacks, after all. And once a working DB Edited costume is in place, visiting a tailor to edit THAT costume slot (one with a lock on it) will lose the DB Edited changes. (Any non-locked costume you're still free to change at a tailor at will.) BUT if you do get stuck with a non-working part, sharing your findings on these boards will get a response from others in your shoes, and possibly an answer.