Ben, Kevin from Forrester wood shafts has 5/16 POC listed with a minimum spine of 30#. If anyone could help I bet he could.
Hildebrand have the same (5/16, 30#)listed but in Douglas Fir and Sitka Spruce.
Lancaster have a ‘kids arrow’ listed too, 1/4″, “suitable for bows under 20#”, 24″ long, complete with fletching and tip for $2.50 a pop.
Jim