Something like this might be a good way to start:
http://www.amazon.com/American-Educational-Classroom-Collection-Minerals/dp/B005QDPZ6U/ref=pd_sim_indust_1
I got these ones and were happy with the results:
http://www.amazon.com/American-Educational-Hardness-Collection-Test/dp/B00657V3NU/ref=sr_1_4?ie=UTF8&qid=1376094238&sr=8-4&keywords=mohs+hardness
They are minerals of different hardness from 1-7 on the mohs hardness scale.
