Is there a tool to search Steam for users with cards from specific sets?

http://www.steamtradematcher.com/

Darn, what he said.
Nice cards! :D

Use the SCE bot: http://www.steamcardexchange.net/index.php

STM and SCE are both good.
Suggest you also check out 1:1 Trading Steam Group
http://steamcommunity.com/groups/honestmerchants/discussions
especially Open Inventory subsection.

http://steamcommunity.com/id/730t/badges/

each individual game badge page will show (unless you got a full set already) whom of your friends own cards of this game on the bottom of the individual pages. well, with only 61 mid range level friends i don't know how successful that can be, but it's a start.

STM only will show you trades for cards of the same game and only if you have duplicates, but it's a major tool for me to complete sets.

To get cards of games you don't already have cards of SCE might be the bot you need. Of course there's a high chance that you'll have to pay the 50% extra credit cost for taking last cards, but I guess it is okay for your purpose. If you're lucky and the bot has duplicate cards of the set you want and isn't full (8 duplicates of a card) for the cards you want to toss at the bot, then of course it's a perfect trade for you.

the swappy bot is also rather handy http://steamcommunity.com/id/swappy , but STM will be best for looking for cretin set as will the trade form of the game hub for each game.

Steamep.com
Also check out stream group: 1:1 trading