I will let you know on the 1800 and 1812 maps I have I will try and scan them this week, let me know if you wish a copy of any of the other dates I provided.
In the mean time try the Galveston Bay Information Centre (Contact the Information Center at (409) 740-4703 to set an archival research appointment) They have some General Land Office - County Maps This set of maps was published by the Texas General Land Office and covers the counties of Brazoria, Chambers, Galveston and Harris. These maps contain information on property titles dating back to the 1800's but also covers the bay itself.
Another place to try is the GLO historical programs, contact the Archives & Records Division at 512-463-5277. The Archives Research Room is open Monday through Friday from 7:30 AM until 6:00 PM (CST).
Texas General Land Office
1700 North Congress Avenue
Archives and Records Division
Austin, Texas 78701-1495