I put an email out to Wapiti but they did not respond. I checked with my friend who used to have a shop. He has 5/16" unmarked cedars, 11/32 ash, 11/32 maple, compressed maple, and both sitka and cedars starting at 60# and up. He even has some over 75#. Unfortunately all too stiff for my bow.
If I can find a spine tester locally I will check the 5/16" shafts but I doubt they will make 50-55#.