It lists the active "in stock" status of quite a few websites. Seems to be pretty accurate for me so far.
This is link that's supposed to be a "real time" ammo update list and says it updates every 60 seconds:
http://www.gunbot.net/index.php?cal=223556
This is another possible link. I haven't researched all the items, but so far the company's I've checked appear to have the ammo in stock at the time I searched for .45ACP
http://www.dogpile.com/info.dogpl/se...id=2&qlnk=True