Just get hold of one of B2 mics with triangle logo and ear in it. It has the right capsule. I am not sure about the newer one which has just the ear logo on it.
You would probably need to build c12 from scratch, but you can also find the original Rode classic schematic, i've seen it around.
Mentioned Nady tcm1050 can be moded to C12 (apex 460 to c12 mod applies), and the body is reasonably close.
What you are asking is a bit outside of my abilities to explain here in detail. But if you use the search function and Google in general to find all the answers.
Start by getting a B2, it is very likely you will be more than satisfied with it stock if you already like the Classic 1.