I am lucky, my farrier is pretty reliable.
Currently both of my horses are barefoot and doing well. They still get trimmed every 6-8 weeks though, depending on the time of year.

I know how hard it can be though when you can't get a reputable farrier, been there before.

Maybe you can take a farrier course and learn how to trim your own, then you know it will get done in a timely manner.