I'm not aware of any Texas units in Virginia other than those eventually assigned to the Texas Brigade. These were the 1st, 4th and 5th Texas Regiments.
Texas soldiers sent to any Federal prison north of the Ohio River could be (and probably were) processed for exchange on the James River in Virginia. The two major exchange points were (1) James River near Petersburg VA, and (2) Vicksburg MS before that area came under Federal military control. Transportation across Northern states wasn't difficult because of the many rail connections. Prisoners were moved by ship to Norfolk-Hampton Roads VA, and from there up the James to City Point VA. Many prisoners processed at City Point VA during March 1865 never returned to their assigned commands.