Pretty much any place that sells wrap or parts for drum building & repair will have a selection of grommets and installation tools. (For standard grommets, you can improvise an installation tool for just a few bucks in the nuts & bolts aisle of a good hardware store.)

http://www.drummaker.com

http://www.drumfoundry.com

http://www.precisiondrum.com

http://www.jamminsam.com

I like the non vintage, threaded vent grommets.

1/2 inch hole or a little smaller. Place chrome, black or brass grommet through hole and put a washer and a nut on it. Done easy and clean.

Drum Factory sells these.

Vintage look requires a vent grommet installation tool for crimping.

I heard Old Kentucky Drum has a good one.

GGD aka scott

Also try Matt at www.drumfactorydirect.com He is small and has top notch customer service and his prices are better than the "big boys". I'm all for small businesses and he just does it right, no matter what. If you have a problem, no problem, he is all over his customers, and very timely shipping. Give him a shot, you may find a new supplier that really cares about drummers and our plight and need for parts on a budget. Mostly sells the the same exact stuff as all the others, so if he is 15% (or more) less, you gotta wonder...what are you paying for at the others, besides more expensive websites?

Direct link to grommets: http://www.drumfactorydirect.com/index.php?main_page=index&cPath=6_62

Whoa yeah - those are perfect. I really like those thread-on ones, thanks guys.

The threaded ones are nice, but they require bigger holes in the shell -- 1/2 inch versus 3/8.

And I didn't mean to leave drumfactorydirect.com off my list. I've bought a few things there and have nothing but good things to say about the experience. (Same goes for drummaker.com and drumfoundry.com.)