Seems to me that publishing as a catalog instead of a shop would be more in line with the type of B2B sales you apparently are engaged in. Bolster the catalog with a good contact form also.

Yeah I was thinking the catalog thing too, but it doesn't sound like "all" the products will be part of that issue and that some things will be purchasable online normally so I didn't bother to mention it. Could be though that maybe that would work, or even a couple different shop entities tied together with links on an external home page will work too. This way you can create one shop for the items that have no need for calling in and another shop as a catalog for those things needing call in.

I would definitely include Scott's suggestion for the custom page to help explain how things work. Since you have a base client type already that you probably won't really need a whole lot of explanation for it probably won't be too bad to deal with. As you say, your customers already know they need to call in and that they actually send you the info on their own too so it should be all good as a catalog for that part.