Hello, I can give you the number of a man who owns Llanwenog sheep, he's based in North Carmarthenshire.
I'm sure he'll help you with finding someone who has some for sale.
Also with regards to the Welsh Black cattle have you tried their website or phoning the secretary, they'll usually tell you the best people to buy off within your area.... as they say its better to start off with the correct stock than buy "rubbish" in and correct it later on.
Hope this all helps