Can I suggest that you get the correct colour terminology before approaching any breeders.
Border Terriers are referred to as Blue and Tan, there is no such colour as Black and Tan.
As for getting a bitch puppy in 8 weeks time, unless you are very very lucky, you will find that bitch's are as rare as hens teeth and you may well have to wait much longer than 8 weeks to get one. I have people on my books now for bitch's and my bitch's are not due in season for another 2 months.