ToME WikiI found a nice website:
[molotov.nu - Game Graphics] http://www.molotov.nu/?page=graphics
This website covers a number of graphic sets. I don't know these materials are free from "Copy right", but it's seems these graphics are created in the cause of "Free" game developing. Anyway, since I had split 8x8, 16x16 and 32x32 graphic sets of ToME module into individual PNG files respectively (look at /Developers Corner/3.0.0 ToDo/Revamp the Graphics), I know molotov.nu - Game Graphics introduces graphics not used in ToME.
In graphics mode, still there are ASCII tile. Maybe we can find a suitable graphic from one of these listed in molotov.nu - Game Graphics (Or we can simply choose a graphic from existing graphic set!).