Amazon, Sheet music Plus, and Shar are good places to order music.  Local music stores will also have most materials in stock.

The local violin shops in Houston are Lisle Violins (multiple locations) and Amati Violins.

Leslie Violins
Amati Violins

Either a piano or keyboard will both work for piano lessons. If selecting a keyboard, it will need a full 88 keys and I recommend one with weighed keys.

Houston Piano Company
Fort Bend Music Center

Houston Youth Symphony
Houston Youth String Orchestra
Katy Youth Symphony
Virtuosi of Houston
Pearland Youth Orchestra
AFA (American Festival for the Arts) – Chamber Program