I have a couple that work on my MP130 and MP2000 but not on my eMate, but I don't remember what kind they are.

Here's a good list of card types. Maybe you can identify what kind it is and label it so you don't get it mixed up.

http://myapplenewton.blogspot.com/2011/02/apple-newton-memory-201-compatibility.html

I miss my Newtons. Gotta fire them up one of these days!