The best place to find information on Mack and First Seed Material is an RPG Maker forum.  Apparently FSM is only temporarily down, there was some troubles with his host and not renewing something and they're giving him the run around about getting it all back and online again.

Just so you know, it is not legal to use any of RPG Maker's RTP's outside of Enterbrain's Maker programs.  I believe Mack's tiles are original so they don't fit under that rule but some of the sets you can find out there that are called Mack have RTP edits in them so you need to be careful.