You should check out http://www.archoustics-south.com/Home.html. They distribute and install the LogiSon sound masking product. We have it installed in our office and we've been extremely happy with it.
They'll handle setups of pretty much any size as well, so I'm sure they'll be able to help you. The main site is http://www.logison.com/Home.html, but the link above is the actual distributor site.
You'll probably soon be reminded that you have to use real names here, but the distributor you linked apparently covers Texas, Oklahoma, Arkansas, Louisiana, Mississippi and Alabama, so Alexandria, VA is a bit outside their territory. They do have an office that does cover Virginia.
Are there any requirements such as contractor licensing, being on state (commonwealth in this case) or federal contract, etc.? Many times government contracts end up going through larger companies who handle all the paperwork but subcontract most of the actual work.