The Q1 was available from Best Buy and CDW online from date of release in the US. It later became available at Fry's. The only place Best Buy has them in-store is in TX. They started that in July IIRC.
The various Amtek versions have been around from several sources online since release.
It would probably be safe to say they are generally available online, not in store. The same is usually true of laptops and tablets. The manufacturers make too many builds of them for the stores to stock every variation. They generally have the fully-loaded models in-store, and the barely-can-get-out-of-their-own-way models, too.
Add to that the fact that the UMPC manufacturers aren't the ones known for their laptops, like HP, Lenovo, or Dell.
It may be surprising that this is the case, but given that it is the case, it isn't surprising that UMPCs aren't well known. Everyone at work calls my Q1 my "little toy".
If Vista's final RTM turns out to be as good as folks here are raving, then we may see a change in who makes them, what their specs are, and who wants them. Even then, maybe not.
People equate computing power with size. (Not those in the know, of course.) UMPCs just don't look like they're up to any sizable computing task. Of course, most people who worry over that only use a browser and an email client.
Go figure...
;-)
Woadan