Nevermind, I'll draw them myself.
If one sets aside 100 tile pages for backgrounds... lets see.... two corridors per zone, except for Capricorn, means 18 corridors. Plus one for the initial spaceflight in... and another for the last spaceflight out... and one more for a bonus corridor in Capricorn.. so I have 21 total corridors needed. Splitting 100 tile pages 21 ways means a little less than 5 pages per screen. But the screen is wider...
Okay, so we could do this. Draw backgrounds at 1000 pixels by 320 pixels in paint, import them. The screen is not quite 320 pixels wide. So we could scroll twice through each 1000 pixel-long terrain picture - once showing the left half, once showing the right half. There'd be some overlap, but it wouldn't be obvious. That gives you a 2000 pixel long picture to draw during flying stages. If it moves at just shy of Vy = 0.25, that's enough for a two or three minute flying stage, I believe. Bosses can cylce through a smaller portion of the same map.
Alright, so now off to draw the backgrounds. Anyone know of a program that would be better for this than MS Paint? I've got photoshop, not sure if that's a good idea here..