[schlagwerk]

Mugen Generals are official combined modes. The instructions are either with the figures involved, or at least it is advertised on the back of the box. For example, Mugen General 3's instructions are on the instruction sheets for Air Leon, Carry Eagle, and Build Giraffet. Mugen Kaiser 4's instructions are with Kaiser Condor. Wikipedia has a listing of various official combos in their Mugenbine article.

You can find the Korean versions of a lot of the Mugen Gattai series on eBay. Trying to purchase them all individually will drive you over your budget fast. Actually auctions show up rarely.
Mandarake also rarely lists Mugen Gattai toys.
Your best bet is to watch Yahoo Auctions Japan for a large lot. Mine was 18 sets for about $100 ($130-140 after shipping). I saw another one for 16 sets for $200. This can also be scary as you need to use a proxy bidding service and need to know enough Japanese to know what you are looking for and to understand the auction listing.


In other news, I have Machine Robo Wedge on the way. It's a guidebook that covers Machine Robo, Rescue, and at least the Mugen Gattai series.