Unfortunately the D10 doesn't support the AM21 HD OTA tuner....
True
...so you are really left with either finding a previously owned H20 (that comes with a HD tuner)...
There are older HD receivers beside the H20 that came with an ATSC tuner:
HDTV DirecTV Satellite Tuners
* DirecTV HR10-250 (HD DVR)
* DirecTV H10
* DirecTV H20
* Hughes HNS HIRD-E86
* Hughes HNS HTL-HD
* Hughes HNS SD-HBH
* LG LSS-3200A
* Mitsubishi SR-HD5
* Panasonic TU-HDS20
* Philips DSHD800
* Proscan PS61000
* RCA DTC-100
* RCA DTC-210
* RCA DTC-210 Supplement
* RCA HD65W20
* RCA HD65W20
* RCA P61300
* Samsung SIR-TS160 (E)
* Samsung SIR-TS360
* Sony HD100
* Sony SAT-HD200
* Sony SAT-HD300
* Toshiba DST-3000
* Toshiba DW65X91
* Zenith DTV1080
* Zenith HD-SAT520
...or purchasing a HD receiver at BestBuy or online.
Best Buy doesn't have Directv receivers in their stores anymore, and why should the OP buy an HD receiver if he has no plans to upgrade his dish?
...With the second option you will have to play the TV input shuffle to switch between OTA-HD & your DTV service & the OTA locals won't show up in the DTV guide...
My H20 was able to integrate the OTA channels into the guide, but you might want to check the user manual of the receiver you're looking to buy at directv.com.
...If you try to purchase a H20, make sure to get the serial number & access card number & call DTV to verify it is indeed "owned" & no outstanding balance exists...
Very good idea. Also, if you get one of the older receivers, you will probably have to get a new access card before you can activate it on your account...