There are 54 different letter combinations, 30 red and 24 blue. As a general rule all of them are common with the blue tokens starting with W being a little scarcer, the red MM token is scarce but not overly expensive, and the key to the set is the red MV token. Back when I started collecting them there were about 24 pieces known. A lot more have come out of the woodwork over the past 50 years and now the estimate is up around 200 pieces. The MM and MV tokens are kind of strange as they don't fit into the normal pattern of the letter combinations. The MM and MV are the only tokens that start with M, and the MM is the only double letter token that isn't blue.
I'll have to look, but there might have been a page or two of these in 2x2 flips in my father's effects. I've kind of ignored them focusing on pieces with copper, silver, and gold. I'll check tonight. Z