I believe there's at least two forum members from the Houston area. @keeperchris
I hope you are able to find your new, used Bolt.
I have a co-worker that had to buy his used Volt from Alabama (I think) last year.
As far as service, there really isn't anything to service, so there is very little experience working on them.
I would suggest that Classic in Sugar Land sells more than others, so they probably are more familiar.
It might be wise to look into a new, new one though, taking advantage of the remaining Federal tax credits.
As for the Bolt vs. Volt question - the better car is a matter of usage and comfort. I am so happy that my wife loves here Volt, because I wouldn't want to give up my Bolt.
For me, I love the higher ride in the Bolt, and find the Volt's bucket seats to be very uncomfortable for long distance.
She commutes about 40 miles round-trip, so is about 97% electric in the Volt (6 gallons pumped in 16 months). I drive more than 50/60 miles probably twice a week.
To the Volt's credit, even when operating as an ICE Hybrid, it gets about 38 mpg for us.
The one-pedal driving is much superior in the Bolt.