Where you located? I've gotten a few set from a guy in the milford area. Can dig up his number if interested
I've got spare 71 plates if you're interested, I'm pretty sure I have a pair downstairs. I'd trade for other plates or sell.
Here's the YOM information: http://www.michigan.gov/sos/0,1607,7-127-1585_1595_52364-205712--,00.html
Edit: I checked and I do have a few single 71s but all my pairs have a 72 sticker on one of them.
I dont think you need both plates. My 57 is registered that way and only uses the rear plate. I'm going to be registering a few others next year, so we'll see.