Theturners workshop may not have exactly what you are looking for, but that is the best place I have found for cellulose acetate. Vincent is great and his prices are really good. Getting active pen turners to give up cellulose acetate is an other option, good luck with that. Also there is a guy from France on ebay, that sells vintage materials. In fact he has a acution for 6 piece of bakelite, that are at an astromical $1350!
I do not have the exact piece you are looking for. Sorry
2 rods, 7 1/8"" long, 15.6mm (0.615 in) diameter. I do not know if these are cellulose acetate or not, but they look very similar to your photo. If interested, please contact me via PM.