Another forum member has DIY zoom lenses using salvaged lens elements and 3D printing housing, threads. There might be a thread about it, but they are also selling them on (German-) eBay.
My experience with 'building" a lens was to first source Elements (find some old or broken camera on ebay, get spares from bill, etc) and just trail and error with an improvised optical bench till you find some combination that works. 3D print the mechanics. Without knowing the parameters of the lens elements it's impossible to do any calculations, but if you buy elements where you know the parameters you might be able to do it. Germanium has a really high index of refraction, so 2 or 3 elements might do it.
If you take the lens off your camera it's a different problem but you can likely just adapt any given lens that you can find.