You might try casting it with one of these products from Reprorubber. I've used the thin poor to replicate micron-level imperfections in parts and surfaces which I then image in a structured light imager. Depending on how much fidelity you need kind of determines which route to take. For the thin pour, no mold release is required. Cures in about 5-10 minutes.

Bruce

https://www.reprorubber.com/