Have you taken some calipers down to your Delrin rod supplier and checked the sizes on their stock. We get Delrin in all sizes from 1/4" up to 2", I just checked a few sizes and they were all within +0.005" and some were better than +0.002". You should be able to find Delrin rod that is suitable and if you cannot I think you are going to have to loosen up your specs because that is the most precisely sized plastic rod I have ever encountered.
An open mind is a virtue...so long as all the common sense has not leaked out.