I agree, the Detroit team M101-2 Supplement is nice. A couple pop up on ebay per year (definition of "rare" is hard to define - perhaps "uncommon" would be better?).
Ebay seller PWCC just sold the set of 100 M101-2s individually and did QUITE well. The Detroit team was a nice specimen and sold for a healthy price.
http://www.ebay.com/itm/1909-13-M101...p2047675.l2557
At that price I'd be happy to sell mine haha!
Rob
