If you go to the Armalite web site they have AR-10 mags on sale. 20 round mags are $30ea if you buy 5 and the 25 are $40 for 5.
I finally ordered my 25 rounders a few minutes ago. Nothing like the fear of another AWB to inspire one to dig deep!
During their 12 days of Christmas sale on the 17th they had the 25 rounders for $30 so I picked up my basic load