Wolfgang,  for your spring needs, try contacting:

  George Emmot (Pawsons LTD)
  Wadsworth Mill, Oxenhope,
  Keighley, Yorkshire,
  England
  tel.: +44 (0) 1535 643733

Not only will this company manufacture any spring to your
requirements, they will also fit it into the barrel for you.

Mark Singleton, in a very wet and windy Lancashire, UK