I actually just started downloading them last week. In total 12.95GBs of stuff, started rewatching some, still awesome. Only place I know is by using torrents. I'll link you to them.
For Complete cartoon series go here:
http://www.torrentspy.com/torrent/62...n_TAS_Complete
For bonus Pryde of the X-Men(another cartoon episode) which was done year before regular cartoon series we are all used to go:
http://www.torrentspy.com/torrent/61...V_M_VHSRIP_avi