Dallas should be a great resource for finding tourneys. I suspect there are multiple FLGS in that area. In fact, I know there are because my buddy used to live there. My recommendation is go to each FLGS with you army looking for a pick up game on Saturdays / Sundays. Chat up the owners and look for fliers. Likely there's even a Facebook group for Dallas 40k fans.
For major GTs they are frequently posted on this thread. Additionally frontline, I think, keeps a running list of ITC tourneys. www.frontlinegaming.org
Hope that helps. See you in the trenches... when my orks are overrunning them...