Another thing you could also consider is euthanizing the rats at the size your snake requires and freezing your own rodents (assuming your breed your own). This would allow you to have a variety of sizes for what you need but is also a lot more work. Breeding your own rodents also requires more time investment, so you have to weigh the pros and cons of each.

My vote would be to either find a local rodent breeder or buy F/T.

Greg