Not a direct answer to your question, but this company could answer your question : http://www.tenringsportsservices.co.uk/
And possibly the NSRA shop would know the answer also.
If you can't source a FWB stock, MEC make one that will accommodate a FWB 2700 action, as do Kepeller.
Also, you might be able to pick one up through the Stirton Web Site from someone upgrading to a third party stock and not wanting to keep the original FWB one for cost reasons.
It might also be worth while contacting Peter Friend at Surrey Guns as he might be able to source one direct from Germany if they are not available UK wise, and I've always found him good with prices in any event.
HTH, Vic Thompson.