I'm not very familiar with MS-DOS games, but I have a bit of knowledge about NES games.
It might be possible that the data you're looking for is compressed. Something like RLE with small modifications wasn't uncommon on the NES, especially for storing level data. What's also possible, is that multiple pixels are stored in one byte. I don't know the exact specs, though it might be possible that if a sprite can only have four colors, each pixel is a palette color index stored in two bits therefore a byte holds four pixels and the palette selector for each sprite is stored somewhere else. The last option would be to run the game in an emulator with a disassembler attached and just search for writes to the video memory, which is probably the least pleasant way.
