The following guitars can be unlocked to purchase from the store in career mode:

Unlockable - How to Unlock

ES-335 - Earn 5 stars in every song on a CD in medium mode.
Les Paul Dbl. Cutaway - Complete every song on hard mode.
Moderne - Earn 5 stars in every song on a CD in easy mode.
Synapse - Earn 5 stars in every song on a CD in expert mode.
Vanguard - Earn 5 stars on a song on expert.