I do not know of a website but the Texas Historical Commission has a free map of Texas in the Civil War and list of the locations of the Texas Monuments. UNfortanately I do not have the address handy but will post it, if you do not get any replies, after I return to my classroom on Monday August 5th.

Oh, Galveston now has one of the markers near The Strand (recently erected)for the Battle of Galveston which you may wish to add to your list.