I can tell you for a fact that the MLS listings in Canada aren't available
for resale. I strongly believe that this is true in the US as well. The
information is considered quite lucrative.
There is some interesting legalese behind all of it. While NAR (national
association of REALTORS) and CREA (Canadian REALTOR assocation) claim to
"own" the listings, I believe they are actually owned by the brokers (ie
REALTORS) selling the house. This means that in reality, the home owner
actually owns the listing and could probably force his/her realtor to make
it publically available, or available for sale, circumventing the somewhat
narrow-minded NAR/CREA.
Karl