This Ammoseek website (and their app that I've installed on my phone, tho that's not necessary) has been a great help to me when I need a certain type of ammo:
They let you choose the caliber, maker and grain weight of the ammo, then they send out internet webcrawlers to tell you which companies presently have it in stock and at what price. They will also give you links that take you right to the page on the sellers' sites. Easy as pie.
Ammoliquidator and Bud's Gun Shop presently have both the regular pressure and +P versions in stock.
If you're looking for local stores, try Dicks Sporting Goods or Field and Stream, or Cabelas. Also, you can find it at guns shows, usually at great prices.