Just out of curiosity could you maybe find a larger scale or medium scale rodent breeder who would be willing to possibly work something out for rodents?
Say a trade?
Or maybe some sort of "advertising" in your store for feeders as payment?
Or maybe a promise/agreement to continue puchasing the large amount of rodents you need from the same location in the future, if they can give you a front on a week or two worth now?
My suggestions sound ridiculous...but my best.