Most of the locations mentioned such as Lake Fork, Lake Texoma, Ray Roberts, Tawakoni and Fairfield have eagles during the winter months, best around February.
They all require a boat to get to where they nest. Otherwise the nesting pair at Llano is accessable with a long tele.
Here is a link to some info regarding Lake fork and Tawakoni.
http://www.eaglefest.org/
If your willing to go north then Quartz Mountain in Oklahoma has eagles during the winter months as does Kaw Lake in northern Oklahoma.