So far they are still rare.
Switserland issued a stamp on wood in 2014. It's an auto-adhesive stamp, protected by a peel-off foil.
|5 swiss francs - 2014 - wooden stamp|
The stamp is half a milimeter thick, what allows it still to be placed on a letter for acutal use.
Unfortunately few will have been put in circulation,
The issued stamp of 5 Swiss francs, is 5 times more expensive that the stamps for regular letters.
Probably it can be found as CTO.
Catalogue Michel rates it equal for mint or postally used.
More to come :-)