Szechuan peppercorn disappeared from US store shelves about a year ago after the (USDA? FDA?) declared them a carrier of citrus canker. Sansho is a powdered Japanese spice botanically similar (but very different in flavor) to the Chinese variation. Until recently, sansho was still available in my local Japanese supermarkets (So Cal), but it seems the powers that be are now seizing sansho as well.
If you have a local source that still sells sansho (or Szechuan peppercorns, for that matter, better grab it while you can.