You should check out rockwool's web site. Indeed they have many products which is suitable for sonic treatment. Although I think the topic poster should ask the same at Ethan Winer's acoustic forum. There are many very helpful people out there.
Regards Tamas Dragon
I'm not in the DC Metro Area - I'm in St. Louis. The OP had asked about web resources also.
If you guys want to get together and do a group order for out there, I'll work with you on price.
For applications, personally, I use it exclusively for broadband bass absorbtion. Now, I only stock the heaviest density material and do so specifically for that purpose. I can get ligher densities on special order (not very popular) and can also get other thicknesses on 1 day's notice.