Hi all,
Here's how I see it.
1) The KR were primarily a military order that was based in Urithiru. It would make sense then, that their armory and primary garrison was located there. Now, in most militaries, there are a certain number out on patrol/remote postings at a given time, while the majority are confined to garrison, especially in times of relative peace. In Dalinar's vision, while there is a border skirmish going on, there is no reason to suspect that a larger war requiring a large deployment was taking place.
2) There is no reason why shardblades have to be permanently bonded to a user. In fact we have seen two cases where they are specifically not: When Dalinar trades his blade to Sadeas, and the custom of renting plate/blades for duels. This could mean that when KR weren't in the field they kept their armor and weapons stored in case they were needed. (As pointed out, Mr. Sanderson said they were available to all the orders, even those that didn't generally use them.)
3) If the above 2 suppositions are true, it would stand to reason that most blades/plate were stored in Urithiru at the time of Recreance. It's quite possible, then, that what Dalinar saw were the only KR in the field at the time. The rest could just have easily left their armor and weapons in garrison and walked away. Since no seems to know where Urithiru is/was, and it may have been largely inaccessible to the general population, I think that most blades/plate are still there, wherever that may be. If you subtract the blades that are held and not known, and those that have been lost over the years (shipwrecks in deep water, etc), I think we can arrive pretty easily at the known number out there.
Just my 2 cents.
*goes back to lurking*