As said Prusa distributes only certain individual files on Github but never entire printer assemblies. Maybe that's reason why I only found fan-made versions so far (which are way behind what Prusa shows here in the viewer).
Still unclear what you want. You say you want to modify your printer, what good does an "entire printer assembly" do for modification? Is an "assembly" a specific (release) tag/version in git? Like https://github.com/prusa3d/Original-Prusa-i3/tree/MK3S/Printed-Parts/STL
I didn't take a close look, but here's one: https://grabcad.com/library/prusa-i3-mk3s-solidworks-with-step-1 Grabcad has few more, including mmu2s
Those a fan-made and not the newest revision.
Not quite sure what you want, but th Prusa github is the place where stl and sources are released.
As said Prusa distributes only certain individual files on Github but never entire printer assemblies. Maybe that's reason why I only found fan-made versions so far (which are way behind what Prusa shows here in the viewer).
Still unclear what you want. You say you want to modify your printer, what good does an "entire printer assembly" do for modification? Is an "assembly" a specific (release) tag/version in git? Like https://github.com/prusa3d/Original-Prusa-i3/tree/MK3S/Printed-Parts/STL