Not common but not rare either. Good ones usually sell for under $40.00. I just finished listing one for the Spring Auction at York, Nebraska (Lot 399).
Patent is on DATAMP at:
http://www.datamp.org/patents/displayPatent.php?pn=1436049&id=48260 (http://www.datamp.org/patents/displayPatent.php?pn=1436049&id=48260)
If anybody is interested in watching the catalog "in progress" it's at:
http://wrenchingnews.com/york-auction-2012/catalog.html (http://wrenchingnews.com/york-auction-2012/catalog.html)
Pictures are stored at:
http://s222.photobucket.com/albums/dd3/buswrench/york-2012/?start=al (http://s222.photobucket.com/albums/dd3/buswrench/york-2012/?start=al)l
(http://i222.photobucket.com/albums/dd3/buswrench/york-2012/Y12-0398-416.jpg)