I'm not sure what you've found already, but here are a few H/J barns I know of. Feather Creek Farm - Hosting USEA Horse Trials, Schooling Shows, Clinics & More!
-never actually been here but I do know eventing is their thing Home page for Fox Lair Farm, Piedmont, OK
-in Piedmont, horse population is around 10 or so last time I was out there, plenty of room. The owner is super nice especially when you get to know her better. For the Love of Horses
-pics are not UTD they are now at the old Hadwell Stables. Loads of room from what i've heard, trainer/owner is fair and runs a clean barn. Easy J Stables
-in Harrah, i've tried 4 horses from this barn, Gia was welcoming and it looked like there was a lot of room, but quite a few horses were there.
There's always Cadence Equestrian Center, last time I was out there it fits everything you want except smaller and more private.