Not sure what constitutes "rarity". There's 4 T210 Stengels in the SGC pop reports and at least a few raw ones floating around; if anybody has access to PSA pop reports and could tell me how many they have enslabulated I'd be obliged. Suffice to say these don't pop up on eBay too often.
Edited to add: This has the makings of a helluva thread. Looking forward to it.