Is there a reason why you want delrin rather than lexan? If you are ok with a 3d print process, I'm sure there are many who would do this for you. Is there a reason you're not contacting the manufacturer of the piece you want to copy for a plastic version? Also, are you not able to settle for a plastic rim? I would start with the people who made the original, otherwise someone is going to have to reverse engineer it for you. May be expensive and inaccurate.
I have played delrin: one of the older DEG "Astro" mouthpieces. I have played lexan, including Kelly and blokepiece rims (my current mouthpieces). I have played all the metals except the esoteric titanium anodized or coated. If you want a plastic rim, it would be less expensive to find a similar 3-piece mouthpiece with a plastic rim than have a delrin mouthpiece made, because delrin and lexan are usually cast, not milled, and when milled, can warp easily in the process.