Links to websites which may be of interest to commercial overprint collectors :

The Perfin Society :

GB Overprints Society :

The Revenue Society :

Precancels of Great Britain :

Protective Overprints and Underprints :  – a revenue stamp dealer who has a gallery of commercial overprints on his site.

No links to any online stamp dealers as I have yet to find one who sells commercial overprints. However, Perfin Society auctions feature overprint material quite regularly. Otherwise the best sources on the web for overprints are and