Need Some Texan Help- Registering as an Antique

[Ole Blue 68]

I thought I was fairly smart till I tried to get antique registration/plates for my truck. I found the application form and instructions that state the following:

"Owners of motor vehicles 25 years old or older that meet the limited use restriction provisions of this registration may take advantage of this exemption by contacting the nearest Texas Department of Public
Safety, Safety Responsibility Bureau. Upon receipt of the affidavit of exemption, the portion of the form designated “FOR COUNTY USE ONLY” will be signed, stamped, and dated by an authorized agent of the
Department of Public Safety. The original affidavit will be filed, and a copy will be returned to the owner."

I've called all over the place and can't find a DPS, Safety Responsibility Bureau here in Houston. What do I need to do?