Street Fighter X Mega Man was brought onto PCs by Capcom so as to count the number of downloads. They could have tested it for Mac based systems, but they never represented it there.
Although, soon after the release on PC, a fan ported and introduced the game on Mac based systems. This unofficial port is based on the version 2.0 of the game.
Here is a link to the .dmg file of the game for Mac based systems.
Source: Destructoid