Jeff Turnbull has commercial overprints that are available for sale--or for trade for perfin revenues of Great Britain or former Commonwealth countries. Here are some examples of the material that is available:
There are also commercial overprints on receipts and some handstamps. Jeff can provide scans.
If you are a collector interested in adding to your collection or a non-collector who is intrigued by this barely explored piece of history, you can contact Jeff at: