I think MSX uses several tile formats.
In the one game I tried to hack, I found tiles were stored in VRAM in a bitplane format.
It stored one plane for the entire tileset before storing the next plane (unlike other formats, which store planes one tile at a time).
So, like for example (8x8 tilesize x 256 tiles = $800 bytes per plane):
address 0 = tile 1, line 1, plane 1
address $800 = tile 1, line 1, plane 2
address $1000 = tile 1, line 1, plane 3
I'd guess if the game used a tile format, you'd probably need to make a custom program to dump/insert the tiles (or at least convert to NES or GB format to make it easier to edit), because it doesn't sound like something a tile editor would be able to easily support (it would need to know not just the address, but also the tileset size to be able to render it).
I remember I found it out by dumping the VRAM in blueMSX.
(as for finding the data in the disk image: if the graphics aren't compressed, you'd need to find matching data in the disk image once you find the graphic data in VRAM)

I think PC98 stored its bitmapped VRAM data similarily.