The main problem thus far (2020) with printable parts is a lack of durability. This isn't an issue for grind blocks or antirockers, which can be trivially reprinted- but an item like a complete plastic frame requires a more expensive printing technique like SLS than good 'ole FDM, or less environmentally friendly filaments (think fancy fiber-nylon) to last very long -- and SLS prints are probably going to be produced by a third party with deep pockets.

But it might be possible to overcome this hurdle by designing parts specifically for FDM, meanwhile leveraging the positive side effects of a ...

Lots of folks are making stuff, but few are sharing recipes.

STLs or it didn't exist?

Open Element 2.0

A model akin to the Kizer Element 2.
Direct Link
https://www.thingiverse.com/thing:3964175
Method(s) Frame: CNC aluminum alloy; Grind Block: CNC UHMW; FDM ABS/PLA/Nylon/etc or SLS Nylon, Alumide.
License CC-BY-NC-SA

Salomon Souls

By Starscream/Claudio A. Sizes for 265/75/85mm boots: scale up or down manually for other sizes. Protects the original boot surfaces with minimal added ride height.
Direct Link https://www.thingiverse.com/thing:4025289
Method(s) SLS Nylon ...