Here's the official word on the belt issue:
Belts can be purchased at any NAPA store as Gates makes NAPA's belts and they use the same part#'s.
Belts Underdrive Kit:
• Alternator / Power Steering Belt – Use Gates K050330 (33 5/8” or 855MM), alternate belt size use K050336 (34.25” or 870MM) *
• Air Conditioning Belt – Use Gates K040315 (32 1/4” or 820MM).
* Return the unused belt to the local auto store based on fitment.
Stock Diameter Kit:
• Alternator / Power Steering Belt – Use Gates K050355 (36 1/8" or 920MM) *
• A/C: Stock Length
* We add extra height on outer side of the front belt and inner side of the inside belt area of the pulley. Subaru does not add any extra material so the outer diameter is the same across the entire pulley. This is why our kit requires a larger belt for the alternator/power steering section.