You would be well served to spend a weekend or two in Austin and Bastrop. I haven't been to Bastrop since the wildfires, so I have no idea about the current conditions or even if the park is open to the public. However, the route through Bastrop and Buescher Parks have plenty of short, steep rollers for you to practice on. I make it up there twice every year once for Pedal Through the Pines and again on my own. IMHO it was some of the most beautiful scenery in the state with all the tall beautiful pines. I've heard that's all gone now, but I'm sure it will be back in a couple of years despite the wildfires.

You could spend a night there and then take off to Austin the next day and do a ride like Dam Loop. If you do the Dam counterclockwise, there is Tumble Weed hill (which stone free mentioned above), a half mile at a 10% average grade. If you do it clockwise you'll get more long shallow climbs. If you're really feeling like torturing yourself, you can tack on a fun loop that combines Courtyard, Beaufort, and Jester which are basically the steepest climbs you'll find in the state. Jester sounds like a carbon copy of what you're going to face.

So basically to answer your question... no, there's nothing in Houston to accomplish what you're looking for... lol. With that said, I don't think you need consistent training on grades that steep to be good during your climb. I was able to complete Tour Das Hugel this year and my usual training loop only has one hundred foot climb over 800m. In Sugar Land, I hit the Town Center Parking Garage and do things like gear progressions and just going as hard as I can. Obviously experience counts a bunch on steep grades so you'll know when your redline is and I think a couple of trips in the Austin area would be great for that. But I'm not sure you need to hit the steep stuff every week to do great in your event. Good luck, let me know if I can help at all.