Another place that may be useful to some is the Beverage Barn on Richmond. Its the drive through liquor store, but they also fill CO2. http://www.bbliquor.com/
Also, Texas Homebrewers at Fry Rd will be filling, but they need to get their regulator fixed, so it may be another week or 2, according to an email I got from them last week. http://www.texashomebrewers.com/
I am currently trying to find a place on the NW side (BW/290), so if anybody knows of anything up that way, I'd appreciate the info.