Yea I'm pretty sure they're unique to the vest used, possibly even made specifically for Disney. The closest buckle that I've found besides what Andy has provided us above can be found her at americanplastics.com. http://americanplastics.com/catalog.asp?cat=829570950&p=4&c=14
Granted the strap is different the buckle looks spot on. This is a TIFCO buckle, other TIFCO buckles can be found used on other parts of the armor as well.