I can't help answer your exact question, however, a 1" dowel rod and some adhesive backed rolled sandpaper works great. Just be sure to clean the sandpaper often as the plastic fills in around the grit. Also, if you ever consider glass bedding a synthetic forend, you're in for a lesson. Due to the content of the "plastics" used, glass won't stick to it very well at all. Earlier this year I spoke to several stockmakers and they all agreed that they would need a minimum order of 250 forends to make it worth the cost to build a mold.
Thanks, Dinny