I ordered 5 compact magazine by way of Ebay -- the magazines are only available with the flat butt plate, I was able to call Smith & Wesson Customer Service:
By Telephone:
1-800-331-0852 (USA)
Mon-Fri 8:00AM-8:00PM Eastern Time
And ordered a few of the one finger groove, butt plates -- $1.50 each plus shipping -- I read on a few other boards that S&W sent one or two for free -- they charged me $21.50 for 10 -- So maybe you can work a deal?
Botach also had the regular M&P .45 full size 10 round magazines for $19.95 -- The cheapest Xgrip magazine adapter I found was on Ebay $15.75 with free shipping.