This is interesting for me to read about large format photographers who just submit photographs to NPS on their own. I think it's great! An important thing to know about HABS is that you are placing your photographs in the public domain.
I found these guys on the internet.
I haven't tried them yet, but perhaps they are a good source for AZO paper?
I'm an architectural historian, and so I do the written data portion for HABS and HABS-like projects as part of my job. Like Kirk said, HABS (if the structure is eligible for the National Register) or HABS-like (if it is significant locally) is often used as a mitigation measure when the building is being adaptively reused (i.e. a fire station is being remade into a restaurant), restored, or demolished.
In California we have a pretty strong law (CEQA) that requires government agencies (including local planning departments) to assess and mitigate the negative impacts their project might have on the environment. Historic properties are considered under the umbrella of environment. Additionally, Section 106 of the National Historic Preservation Act of 1966 requires federal agencies (i.e. Federal Highways, Millitary etc) to do essentially the same thing, but just for the national register. HABS projects generally come from these sources, and people like me are often the ones writing the mitigation measures.
This is a big reason that I'm getting into large format photography, so I can do another piece of the HABS documentation when my company prescribes (and then is asked to do) HABS as mitigation for a project. As I learn more about Large Format photography, I'm increasingly appalled when I photograph for HABS-like in 35mm. It doesn't seem like it would be that much more expensive to do large format and scan it, and it would be of WAY more benefit to any future user.