Ask Mr. Smarty Plants

Specific GPS coordinates? Nope, sorry. However, let us first tell you what we do know about Castilleja indivisa (Entireleaf indian paintbrush). According to this USDA Plant Profile map, it does grow natively in your area of North Central Texas. From a previous answer, in which all the links have been updated, should help you more than any other source we have at our disposal:

"To our knowledge, there is no one comprehensive map site showing when and where the wildflowers will be blooming. The reason for this is that the wildflowers are in charge here, and they don't read maps. They bloom when and where there has been sufficient moisture and where their habitat is undisturbed. 

The Lady Bird Johnson Wildflower Center Wildflower Forecast has just been released for this month. Several other groups provide information on sightings and routes for viewing wildflowers. One of these is Lonestar Internet, Inc.  DeWitt County offers its own wildflower site as does Brenham, Texas in Washington County. On the Brenham page, select "Visitor Information", then "Wildflower Watch" to find their information on wildflowers. There is also a Texas Highway Department website  Wildflower Sightings. And you can go any time to the Wildflower Center Image Gallery which will always have pictures of flowers currently blooming, year round. 

From Our Native Plant Image Gallery:

Castilleja indivisa

Castilleja indivisa

Castilleja indivisa

Castilleja indivisa