Like mouse says, your best bet may be to try 
Fine-Toon gallery and Planet Anime, though I doubt 
you'll find anything either place.  Fine-Toon 
really doesn't carry anime, and what little they 
have is monstrously overpriced (in my opinion).  
The whole "investment quality cels" atmosphere 
there is a real put-off.

It's been awhile since I browsed cels at Planet 
Anime.  I've been an occasional customer of PA 
ever since they opened, but in all that time I've 
only bought one cel from them, *years* ago.  The 
prices are never that great.  I'm not even sure 
they still have any cels.  They used to keep them 
in Itoya-type cel books, just sitting out stacked 
up flat on the counters for any and everyone to 
paw through and manhandle.  I haven't seen those 
cel books for a long time.  Hopefully, 
they're keeping them behind the counter and 
storing them in a less destructive way.  Still, 
the shop is worth a look, if only for the anime 
goodies and not the cels.

I don't know much about other cel collectors in 
Houston (other than myself, of course).  There are 
bound to be some, I'm sure.