The first two are there already
Capcom and Sumthing Else Music have combined forces to bring the first four Mega Mansoundtracks to iTunes. Right now you can grab the first two, released as “Volume 1” and “Volume 2” on the storefront (Mega Man 1 and 2 respectively), which contain original NES tracks as well as the arranged versions from the Complete Worksreleases.
On July 29th, both Volume 3 and Volume 4 will hit iTunes.
Mega Man Soundtrack (Vol. 1), (Vol. 2) [iTunes via Rockman Corner]