Not sure if you're still looking, but a friend of mine did that when she got married in march. She just called a few different Chinese companies and found a company that would do the flip flops for $1 each. They chose white (think that's the cheapest) with pink writing for the couples names and the date. They even got their names punched out of the flip flops so it left 'jicky's' (it's Jimmy and Vicky combined) all over the sand while people were walking. They ordered 80 pairs I think.
I think she just looked/researched online, found some wholesale companies and called them up to negotiate a price. She did all this from Australia, but I'm sure you could find some company's in the states.
Hope this helps!