You can order it online at DIRECTV's site for $50. If you have an HR21 or HR22 in your current setup (Follow "My Setup" tab to "Current Setup"). You should see a link for the AM-21 "Kits & Equipment" under "Shop DIRECTV" on the right of the screen.rcodey said:
Incidentally, I recently had a free upgrade from an HR10-250 to an HR21-100 and I got a CSR who had never heard of the AM21. I walked her through how to find it on the web site and she was able to order one for me free of charge.
I also have one on my HR22-100 and it works fine. FYI Perhaps what the CSR meant is that the ordering system is down?