Hi Madmx
I agree with Stavros, give MMB or Ron a ring for a good quality brass prop, but if you after a bronze one then prop shop is very good. Like you say the sizes are a bit odd, it took a little while to work out what they were on about but I think I've worked it out.
The first two numbers are the diameter eg 20 being 2inches
The second two numbers are the pitch eg 22 being 2.2 inches
Prop shop say there are several anomalies with their system and have labelled them under the Product and Services Section of their website.
Hope this helps, I'd just give them ring if possible.