How to find a good sweet potato fry cutter?

I have the Progressive International Jumbo Potato Cutter and it works well for sweet potato fries. The product spec for them lists "Yams" which are sometimes what sweet potatoes are called in the U.S. (technically, yes, yams are different but real yams are not often available in the U.S.). The LEM Products Commercial French Fry Cutter specifically lists sweet potatoes:

Makes French fries, sweet potato fries, zucchini sticks and other favorites

Ziggy's Potato Cutters will handle sweet potatoes...they are harder on the blade but it does a fine job. www.ribbonfries.biz

You can improve the operation of the sweet potato cutter by microwaving the potato for about a minute and cutting off the ends to square it up against the blade. And don't try to cut with one push. Rather a series of less forceful pushes pressuring the potato a little bit at a time. Don't be afraid to use PAM on the blades to reduce friction. Good luck.

Most varieties of sweet potato will not successfully chip, or hold together during the cooking process when chipped into the traditional square rod shape. Sweet potato turns mushy very quickly during the cooking process, and may also go very chewy if even slightly over cooked

Commercial sweet potato chips have been carefully selected and pre-cooked to hold shape and maintain strength for the a quick hot oil fry finish. Frozen sweet potato chips are generally intended for cooking in the oven

I would suggest you experiment with different sized discs cut from the width of the sweet potato. Using an adjustable depth Mandoline will help with this