I have worked at a few gaming conventions. (Games are my hobby.) If you're interested in some door prizes, call or write to the game companies directly. (Look online or on the back of the boxes.) We always had tons of prizes that way. Also if you offer to try out a new game, they send more prizes (that game and its promos) and may even send a rep to teach everyone how to play.
Something to consider with an older group is that the card games - Yugi-oh! and Pokemon are very math intensive, so is WarHammer. (They are also quite popular. But you have to make a rule that it's just for fun, some people play for cards like the old marbles game played for marbles.)
Strategy games like Civilization and History of the World teach geography and history as well. Steve Jackson Games has some fun games - RoboRalley is a favorite (You "program" a robot to navigate a dangerous factory). Power is a good beginning strategy game, it's very colorful too.
I don't know if those are outside the age level you're working with, but they're great games that disguise learning math, history, logic, even grammar if you have to read rules off the cards.
How we did the gaming room:
We had someone host each game to make sure it went smoothly and to teach newbies the rules. We asked anyone who won the game to host another that night or another time. They were usually so flattered, they didn't realize they were getting recruited to volunteer.

Make sure there's enough space between the games - a noisy group will disprupt the next game. Have decks of cards or something to do for people who are waiting.
Call anyone who can teach a game - game stores, chess clubs, senior centers often have bridge, cribbage and other game groups that can teach you a new trick or two.
Variety will keep people coming back. Many game stores - not Toys r Us, but Card and Game stores have a game "Library" that you can borrow from if you don't have enough variety on your own. The PTO/PTA should not have to buy any. They will probably also have a large variety of learning games.
If you are in Colorado, the best store that has all of this is The Game Castle in Loveland. They have games I've never seen before (impressive

).
I've always wondered why games weren't used more as a teaching tool. It's good to see them being used.