I ordered mine directly from the manufacturer:
Lamin-x.com - Protective Films
$21.90 shipped for 2 pieces of yellow film. It turned out, with careful cutting, that I have enough for 2 sets of fogs, so I have some to spare in case I need a replacement.
If you can get pre-cut for the same price, then no big deal either way. Since the fogs are so easy to remove for fitting, cutting your own is very easy.
JonasM