I keep a modest selection of violas from 12” up to 15.5” The smaller sizes are more entry level and get progressively higher in quality with size ( by the time you grow into a bigger viola you want something a bit better). I draw from the Neo, Neo+ and Encore range of Vivo instruments for these. I can also order in the fabulous Piacenza Viola and Hidersine reserve viola which will do most players through high school and into tertiary study of the instrument.
Violas tend to have a wider, deeper body than violins, to support the resonance of the lower notes they play. However for the smaller size viola, some people use violins that have been strung as a viola. These work quite adequately in the beginning stages of learning, though necessitate adjustments to nut, bridge and sometimes pegs to accomodate viola strings.
I also keep a ramge of accessories for Violas including bows and strings.