Here's a pretty good one:
http://www.weddingclipart.com/wca/home.do
Maybe consider marthastewart.com
In her website, drag down to templates & clip art. Then in the search bar, type in wedding clip art. Hopefully you may be able to find what you need.
Additionally, there's a really good software program known as Printing Press (available through www.mountaincow.com ). The software contains clip art. It's a very inexpensive software program (Either Printing Press or Printing Press Wedding, either for 29.99...that's all you need. Both contains wedding) and great for creating invitations of all occasions (including weddings); it also maintains a guest list & mailing list too. I've had it for several years, and use it quite often for many occasions.
FYI ONLY:
For card stock, any craft store is good, however, I use this one alot for invitations:
www.paper-source.com
Hope this helps you out! Best Wishes too!