To get the Maibastu Thunder you have to be driving a Cuban Jetmax on land; this is only possible w/ the wheels that you get from stealing the Cessna (not the seaplane, the banner plane ) and landing on top of the Cuban Jetmax while it's in the Boatyard. Then drive it around and you should see a car that looks like a Rancher/ Stinger hybrid. That's your Maibastu Thunder.
Yeah, I saw that " you need to get in the plane with the banner' but then I thought *Hmm, that's odd, they are non-colideable* and then I saw that you needed more crap and then I laughed. A pretty pathetic laugh, too, might I add...