How to keep frozen French fries crispy?
Most likely, your issue is that your fries don't freeze quickly enough!
First of all, potatoes are VERY tricky for freezing anyway: their cell-structure takes REALLY badly to freezing, making them change texture and sometimes taste a lot.
The problem is reduced, but not removed, by cooking them first, but even then, they tend to react badly.
Now, what do commercial fries have that you don't? They can actually do shock-freezing! This means they can freeze their fries REALLY quickly, which highly reduces the damage to the cells. So, sadly your best shot may be: buy some dry ice to use for freezing your fries.