I'd like to see you try the Corian with the new(ish) PSI Everyday Classic, which has a super smooth Schmidt click mechanism.
The finished barrel size should fit nicely in the half-inch Corian ... matching hardware size is about 0.440" diameter, so well within the constraints imposed by your half-inch thick Corian. . You'll have to be careful how you drill it. . I suggest you drill on the lathe after rounding the blank.
Another pen kit which would work is the PSI Duraclick EDC - also has a Schmidt clicker, but a slightly different one ... also super smooth.
This finished barrel size would also fit ... matching hardware is 0.455" diameter. . This kit barrel is a little shorter than the first one so maybe managing the rounding/drilling process would be a little easier.
Check them both out on the PSI website, where the barrel lengths are specified .... should help you choose.
Hope you have some Corian with appropriate color. . Good luck with your project, and be sure to show us the results !!!
I am going to watch this thread !!