You can find specialty doughnut-making equipment at most kitchen supply stores. Here are a few additional suggestions to help you along:
Bob’s Red Mill Natural Foods
Specialty flours (including gluten-free)
Crate and Barrel
Thermometers, pastry cloth
King Arthur Flour
Specialty flours (including gluten-free); doughnut cutters, pans, makers, mixes; glazing sugar; pastry cloth
Sur La Table
Doughnut cutters, pastry bags, astry cloths, pastry bag tips, thermometers, deep fryers
Target
Doughnut pans and droppers, deep fryers
ThermoWorks
Thermapen thermometers
Williams Sonoma
Pastry bags with filling tips, deep fryers, thermometers, pastry cloth, doughnut cutters