These and other Ohio tax stamps can be found in the Start Revenue Society Catalog. However, this area is becoming more popular and the catalog is now sold out with the next edition being scheduled to come out in 2012.
The SRS site;
http://staterevenue.org/The SRS catalog list all state revenue stamps for all states, including DC, by state. New state revenue stamps are still being "discovered".
These stamps are priced like all others in that quantity, condition, mint or used all play a role in the cat. value of the stamp.