They can eat bigger than you think they should be able to. They can eat 1.25x the size of their body's thickest part and are made to stretch a bit. Are the pinkies you're getting almost fuzzy-size?

Not sure what your store budget might dictate but you could order from a website like rodent pro or if there is another pet store in the area, try buying from them? Is your manager able to override or approve anything like that?