There is very little information online, I don't know why. It seems that an important topic has been skirted around. Maybe I will understand the lack of interest once I actually try it!
Anyway, my scanty findings seem to indicate that any non-toxic leaf can be used. I've found a reference to using ash and linden trees, so that is what I will try first. I've got to find some food grade muslin, much tighter then cheesecloth.