Try:

www.lumens.com
www.formplusfunction.com

Another way is to peruse manufacturer's web site and if you see one you like, find a dealer in your area or online. Be aware that a lot of lighting houses will not have much in stock and you may have to order from just a picture in a catalog or online. Here are some manufacturer's to check out:

www.lbllighting.com
www.techlighting.com
www.brucklighting.com

Also, if you find something you like and it appears that it may be for a track light system, some manufacturer's have a mounting system to adapt any pendant to a single ceiling box, such as Tech Lighting's Free Jack system.

Here is one of my favorite sources for
Pendant Lighting

Not just modern or contemporary, they have all types.

Besa Lighting has a great selection of 12 volt and 120 volt glass pendants. Tech Lighting is a great source. They will have dealers listed on their sites or you can do a google search for a dealer.

there are some good options at

Here is a link that might be useful: Lighting So Exciting/Art Glass Lighting

Another vote for Besa here. I was in love with a pendant from LBL, until I found out the cost. Besa had a pendant that I now think is so much better suited to my style and taste, for half the price. But LBL has beautiful lights and a large selection, so you should check it out, as well.

There's a shop I visited today in Charlotte, NC (on E. Morehead) that had lots of cool pendants.

Here is a link that might be useful: Metro Modern