Magazines for this pistol seem to be widely available, but here's a good price of under $30 each. Shipping is a flat $15 though, so you have to order a few to make it pay off. Good service--they shipped the same day to me:
CZ 11520 CZ P-10 9mm 15 rd Black Finish
CZ 11520 CZ P-10 9mm 15 rd Black Finish