Keep in mind that the bulk lots of ammo tend to ebb and flow rather greatly.
There's not much XM193 or M655 out there right now at decent prices like there had been even two or three months ago. That's because the production run is now sold out. Same thing with imported ammo- when a shipment comes in it's everywhere then you never see it again (a while back I remember seeing a ton of Centurion branded ammunition; it was great stuff and by the time I realized it was worth stocking up on it was all gone, never to be seen again).
Factor in the usual "if things are uncertain, buy ammo" and the increasing numbers of gun sales, and it's a recipe for somewhat tighter supplies. However, I've not seen anything like it was in late '08/early '09, when you couldn't buy .380ACP for anything and most other calibers were in extremely short supply. There's ammo out there for everything, but it may not be exactly what you want or the price you saw a few months back. In other words, like it usually is.