For a more recent set of links, see here:
https://forum.vintageairgunsgallery....d-information/
UK shops:
http://www.micksguns.com/air%20guns.htm
http://www.kirklees-guns.co.uk/Secon...Air%20Guns.htm
http://www.guns.gb.com/#1X0
http://www.henrykrank.com/
http://www.dowlings.uk.com/acatalog/...SELECTION.html
German auction site: http://www.egun.de/
US dealer: http://www.pilkguns.com/usedguns.shtml
US vintage forums: http://www.network54.com/Index/47796
Spanish collector: http://www.terra.es/personal3/africatwin/coleccion.htm
Another Spanish collector: http://www.airecomprimido.net/joanaire/