Several years ago I had a firing pin break on one of my 75Bs. I called up CZ USA and Mike Eagleshield, the gunsmith, sent me one, no charge. The pistol was at least 10 years old at that time. So as was suggested above, call CZ USA, they might just help you out.
BTW, that firing pin was the only one I ever broke in any of my many, many CZ pistols. Now a days, I use the CGW extended FP for even greater reliability.