This is what I recently posted in reply to a thread called 'is it bad to get a kitten in a private sale?'
Yes, very. Because you are encouraging people to bring more cats into a world where there are already far too many. If no one bought privately there would be fewer irresponsible people allowing their cats to breed.
Yes there are waiting lists at the moment, but that's because we are still at the start of the season really. There are two seasons - Spring and late Summer. The Spring ones started appearing in March, and gathered pace in April and are still being born now. BUT, they can't leave their mum until they are at least 8 weeks old and preferably ten. So the earliest ones are only just becoming available now. And of course there is always pent up demand over the last few months. However as time goes on, more and more of the April and then the May ones will become available, the pent up demand will fall, and by late June there will almost certainly be more kittens than homes.
Then, when the late Summer ones come along, most of the people who wanted kittens will already have got them and it will be even more difficult to find homes for those. So I know it appears at the moment that there aren't too many kittens being born, but it's an illusion. If you buy, you are being part of the problem and not the solution.
So just be patient, or try other rescues. You can find a list of all of them, including smaller ones, here www.catchat.org