I am assuming that your TV you wish to connect is adjacent to the Motorola 1225 receiver? And that the Moto receiver is fed via HPNA/Coax?
If the answer is yes, the Moto receiver can act as a HPNA/Ethernet bridge for you -- run an Ethernet patch cable from your Smart TV's Ethernet port to the Ethernet port on the back of the Moto receiver. That should provide the TV internet access over HPNA via the Moto reciever
If you do wish to pursue the HPNA/Ethernet bridge adapter route, the model (some) U-Verse techs carry is a Motorola bridge unit (»www.motorola.com/Video-Solutions ··· er_US-EN
HPNA (in this case, over Coax) is an established standard, so any HPNA/Coax bridge device should be compatible with the HPNA port of the 2Wire/Pace 3800. I know Actiontec and Cisco make HPNA/Ethernet bridges, and other companies probably do as well.
Make sure any bridges are actually HPNA/Ethernet and NOT MoCA/Ethernet (MoCA is a competing LAN over in-house Coax technology, but HPNA and MoCA are NOT compatible)