You can start with
Texas Department of Housing & Community Affairs - TDHCA it will apply for anywhere you purchase in Texas, new or preowned.
Some lenders have programs where you have to take their own class to qualify.
Grants are usually for police/fire dept. personnel, teachers.
Some cities such as Frisco give down payment assistance if you live and work within the city of Frisco.
It seems that you have already identified where you want to buy, so the next step is to see what that particular city or county is offering. Connecting with a reputable lender, I would suggest a broker vs a bank in your case if you are looking at getting some financial assistance.
Corinth, Lake Dallas, Argyle, Double Oak, Little Elm, Ponder and Sanger are cities that have most of their areas qualifying for the USDA program. This is a zero down program with a few requirements of which some are:
Must be primary residence
Must meet the limited income (you can't be rich

)
Must attend a class
NACA (Neighborhood Assistance Corporation of America) is another one that offers classes. I don't see one on their schedule but you can sign up and they'll notify you.
https://www.naca.com/index_main.jsp?language=null
Good luck,
Naima