If you're looking to rent a violin/viola, or for strings, repairs and other instrument needs, I find these violin shops are easy to work with and have good quality instruments. 

Violin Shops:

A440 in Roscoe Village
Midwest String Rentals, downtown Chicago
Michael Becker Violins, Park Ridge
Kenneth Stein Vioins, Elmhurst

Suggested Reading:

Helping Parents Practice, by Ed Sprunger
Teaching from the Balance Point, by Ed Kreitman
Time to Practice: A Companion for Parents, by Carrie Reuning-Hummel
Nurtured by Love, by Shinichi Suzuki
Practice Perfect: 42 Rules for Getting Better at Getting Better, by Doug Lemov
Peak, by Anders Ericsson

Misc:

Here's a cool TedTalk about what an amazing thing music is for your brain:
How Playing a Musical Instrument Benefits Your Brain

A blog by a violinist turned psychologist, lots info on how to practice and perform at your best:
Bulletproof Musician