i would look on the adoptions page of this thing or look at your local animal shelter. but somethimes ones from the shelter are hard for first time rat owners. so if you dont have experience i would check to see if you have breeders aroung your area as well.
We prefer to adopt pups and raise them ourselves. As our local pet shop sold over 100 rats per week and closed they left a vacuum behind and left us in search of a new source of rat pups. I called all the listed breeders in our area and they didn't have what we wanted so I called pet shops and was eventually introduced to a snake breeder that was also breeding his own strains of rats... Really nice rats, I might add... We adopted Cloud last year and she's a blazed blue capped silky rex dumbo and last week we adopted Misty... A three week old blazed caped dumbo with really soft straight fur that's that was grey blue but is changing to tan.... she looks almost lavender now.. strange but pretty... I treated Cloud for mites, and Misty is scratching a little, but otherwise they have great personalities and Cloud is nearly a year and a half old and is in perfect health; a bit portly, but not fat. His rats run on the small side, but if they don't get mammary tumors, it's a great trade off.
For the most part, I don't like to support BYB's. But this fellow is supposedly a reputable high end snake breeder and he takes real pride in the rats he breeds... Although I'd like to see him use his talents only for rats, I have no problem with adopting great rats that would otherwise become snake food.
I also found a another snake breeder that bred some hairless rats on the side, but hairless rats aren't my thing... So if you really can't find rats through the normal rat channels look into the reptile world... People that breed high end snakes, or fish or farm animals can usually breed high end rats too and one obsession tends to lead to another.
Our breeder actually seems genuinely happy to see some of his best work go to good homes and so far I'm thrilled with the rats we have adopted. I've referred someone else to him and she got a really sweet and healthy rat too...
On the down side... the breeder I found doesn't overproduce rats, knows what he has and is definitely not cheap when it comes to his top shelf 'fancy' rats... but if you find someone like him, the rats are worth every penny.
Good breeders are out there, they may not be easy to find, but the reptile folks have more contacts than most of us will ever have, because they "consume" way more rats than our fancy does. And the same gifts and talents that produce high end herps also produce high end rats because people that are really gifted at breeding animals take pride in their accomplishments and take good care of all their animals.
It really is a strange world. I hope find the rat(s) you are looking for.