How about making them by cutting slices from a PVC pipe?How about a sail maker?
Of course, if you want to make it look old and classy, why not pick up a few wood embroidery hoops in the 3 inch size, about $1.50 each on Amazon at;
http://www.amazon.com/Darice-Wood-Embroidery-Hoop-3/dp/B001B9I2ZY/ref=pd_sim_ac_6
Just an idea.......
Greg