Tim J
The 222 1/2 is a wildcat. There are no standard dimensions so any cases that someone sends you will be whatever that particular shooter and/or reamer grinder thought it should look like.
So, take Charles' advice. Contact your favorite grinder. He will probably have more than one reamer print in his files. Tell him to pick the one that he thinks is best and make you one.
Advice - if you stick with one that has the same shoulder and neck dimensions as a 222R, you won't have to have special dies made.
JMHO
Ray