There are somewhere near 10,000 nilghai on the King Ranch. It's around 800,000 acres, if that's big enough.
I've lost track of the situation on the YO ranch near Kerrville. I know that they used to have hunts for exotics.
You might try these folks:
http://www.texas-wildlife.org/contact Good organization.
And,
http://www.tpwd.state.tx.us/