I have a similar situation in my business (temp services)
When a customer calls me and asks for a particular type of person, I need to be able to search through 10's of thousands of resumes in my database. So if you look at the resumes as documents (which they are) then your stuff isn't any different than mine.
What you want is a document Retrieval package that ties into an OCR program.
My solution isn't designed for the real estate business. its more designed for recruiting firms.
But, the process is the same. I use OpenCATS. Or you can just look up
http://www.catsone.com (candidate Applicant Tracking system)
I just looked at this and it might work for you.. you can talk to them to see if it's adaptable. I know it's solid.
You can also look at this, it might work:
http://www.rapidlegal.com/whatwedo/research.aspxIt's designed for the legal industry but might work for you
Another is this one
http://www.docuvantage.com/document-management-basic-tutorials/document-retrievalSeems a bit more generic.
Anyway, they are all basically the same, you scan a document, OCR it, store it and then at some point the system refreshes and the document can be found by using a boolean search string.
For me, I might use something like this if I was searching for a .net programmer with Ruby on rails in the 216 area code:
".net and Programmer and Ruby and 216"
I might get a person that lives in Apartment 216 in kansas somewhere but those are easy to pull out LOL
It's all about using word search. And some of the programs out there have the ability to populate a series of fields that may help you (opencats has that) Some of them are customizable so you can set them up anyway you want.
The trick is to find one that does what you need it to do and is within your budget.
OpenCATS for instance is the free version. So all I had to do is download it and it's resident on my desktop and I have a 2 TB external hard drive for my data storage and a back up off site. Works well for me going on 7 years now.
Oh,, as for scanning, I have an Brother MFC 8480 DN with built in software, but for what your looking for, you might need a way more heavy weight set up..
Hope I helped...