I think Custom Stocks of Sheffield can make one for you, otherwise there is the very expensive one that Maccari at ARH in the US which occassionally comes up for sale.
Like this ...
http://www.airrifleheadquarters.com/...83/9984083.htm
They are on sale at the moment, £160 but remember you will have to pay post and import duty so it will be well over £200.
If you have little money and an old, battered Feinwerkbau action needing a stock, as far as I remember the BSA Super Sport stock fits the cylinder diameter OK, you will have to modify it a bit though. See if you can borrow one first and see for yourself what needs doing.