I think I know where to go for the cartridge but it's taking me a bit to find the information. In the mean time, here is an article about a man who built one and took it to Africa. I've met and spoken with him and even got to handle the rifle. But he made his cartridges from barstock so he won't be able to help.
The best I can do right now is to suggest posting on this forum and wait for an answer. I'll keep looking, it's here somewhere!
[ 10-12-2003: Message edited by: Crispin Goodall ]