Were can I get some 5/16 cedar shafts spined 50-55 would prefer a sponsor but I do need some so I'll go were they have them.
Those might be kind of rare for a 5/16" POC.I have had Norway pine 5/16" in 40-45 and 45-50.The highest spine in a 5/16" POC I've seen was around 35-40.I've seen 5/16" ramin in higher spines.You might have to go with 11/32 for POC.
Got some stiff 5/16 from Rose City-a few years ago, some were 50# on my tester and they had been hand picked.
I too would suggest 11/32.
I got some from the Footed shaft, and I had some tapered from Rogue River. What it takes is to have someone that is sorting and spine checking a 1000 lot of shafts keep them for you. They tend to be heavier than the average 5/16th shaft.