The recipe calls for a blend of flours 140 30% brown rice, 30% white rice, 15% tapioca starch, 15% potato starch, 5% potato flour, 3% xanthan gum and 2% powdered pectin.
Ignore the 140. That is a typo. Sorry.
Hi Colleen, Trader Joe's GF AP Flour has whole grain brown rice flour, potato starch, rice flour and tapioca flour as ingredients, listed in that order. I am not sure if you want to try the product or if a TJ's is near you, but I have baked with this flour and my GF friends have said they are happy with the result.
Interesting discussion here that could help
I'd probably try cornstarch or increase the tapioca starch.
In this case, Colleen is asking for a replacement for potato flour, not potato starch, which is also included on her ingredient list. What I took away from the King Arthur Flour discussion i linked to above is that potato flour helps keep baked goods moist--so one option is to leave it out and slightly up the liquid.