Welcome to the world of ratties!
Check out the North of England Rat Society breeders listhttp://www.neratsociety.co.uk/html/breederlist.shtml
There's a show coming up and it'd be well worth going along if you can, it's
Saturday 17th December 2016 at:
St Bartholomew's Church Hall
3 Station Road
Newcastle upon Tyne
Doors will open to exhibitors at 10.15am. Rats should be benched by 10.45am and judging will start at 11am prompt. Non-showing visitors are encouraged to arrive after judging has started.
It's worth waiting for breeder rats, or rescues are another option. There's a facebook group called "rat rescue network UK" that has rats available through no fault of their own.
Pet shop rats on the whole, especially pets at home, are bred in bad conditions with no regard for health and temperament issues so many people prefer not to support that.