Frozen rats are available through a few places. I am aware of Perfect Prey, Big Cheese and ColdBlooded Cafe. Big cheese is my go too. $29 flat rate on shipping and I have been happy with them. Never bought from Perfect Prey however they are respected on this site. Cold Blooded looks great, good prices but only ship on Monday for my local. My timing and needs have not lined up.
I know there are several more and some one will chime in, I’m sure.
Rat color has not been an issue however I have switched over to F/T as soon as I could with my snakes and when live I had a few color variations that really did not become an issue. Usually swallowed down in minutes of offering.