I've had good luck with Steve Sidki, who is based in UK but has a stock of stocks-to-be in the US as well as UK. Clients include H&H, Purdeys, AA Brown, L Bosis - pretty blue chip crowd. A bit expensive but his wood is properly seasoned and he will replace if it is defective. Go to his "Guns Gallery" for examples on guns:

http://www.gunstockblanks.co.uk/index.asp