If you're thinking of buying a cerval/serval cat then obviously there are just the main things to think about when buying a cat from breeder.

Make sure they can be seen with both parents
Make sure they're a well socialised kitten used to handling and being with people.
They should have healthy clean eyes, nose and bottoms.

They should come with a certificate showing their details, and the breeder should be a member of a breeding club, council etc.
So you know that the breeder if following regulations and everything is done properly.
The main thing is that the kittens welfare is paramount and if they're a good proper breeder they will have healthy kittens.

Good luck in your search. I am not from the area so can't give you any tips on where to find one however, I hope the info helped if you didn't know these things already.

Have you thought about having a good old lovable rescue moggy if you can't find what you're looking for?