I use Big Cheese as well and ran into the exact same problem two days ago. Not only do they not have anything larger than a small rat, but he told me they were 2000 in the hole on medium rat orders.
I ended up placing an order with The Mouse Factory and got my order through Greyhound last night. They were a bit pricier, but the quality and customer service are second to none. The rats were all vacuum packed with meat trays and NOT ONE of them had aspen or feces on them. Not even the fuzzies! I was so impressed with my order I may go with them from now on regardless of the price difference.
Good luck with whoever you choose!
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Jason Gonzalez
reMeditatedMorphs@yahoo.com" target="_blank">PreMeditatedMorphs@yahoo.com