Quoted from GRB1959:If the original custom metal die is indeed lost to time then another artist would likely need to create a new custom metal die.
Several years ago, the artist who originally made it said the dies no longer exist.
https://creditdotpinball.com/2014/05/22/mods-foiled-again-the-white-water-topper-reproduction/
From the comments in that article, it sounds like he might be willing to do it again, but it didn't sound like it would be cheap to have done.
Travis of the now defunct TwistedPins attempted to remake the topper, but it wasn't quite like the original. Here's a photo of the embossing die that was made early in the process: