There is a great RV supply place right in our area that has round stainless sinks in two sizes. For you other folks reading this they are also an Internet based RV supply company. Take a look at the following website, click on the index button on the left side and then click on sinks.
Neither of the two sizes are particulary large though so they might not work for a kitchen sink. The prices are not too bad considering they already have the drain hole cut out. Posted prices are as follows:
10-3/8" overall diameter = $25.10
13-5/8" overall diameter = $47.55