I must have 75 - 100 shots out of my current flint and it is still working fine. You must be doing something wrong to only be getting that many shots. Is your flint adjusted correctly? It should be about 1/16" away from the frizzen at 1/2 c0ck.
Is your frizzen loose enough? Does it fly open when the flint hits it?
Are you changing you flint because you are not getting spark? Do you put gun oil on the face of the frizzen? If so, do you wipe it off with alcohol or other degreaser prior to shooting? I prefer to never put any type of oil on my frizzen and a tiny bit of gun grease on where the pivot point and spring meet.