3D printing would be the easiest as long as you have the file. if you have to create the object(s) it all depends on your skill with the software.
If you were to mode it the conventional way, I would cast a large chunk of resin and put it on the lathe until I get the shape of the main grenade body. The greeblies stuck to the grenade would probably be made by a search through my spares box. Small tank wheels might be able to be glued into a master with some additions and then several copies cast. The "handle" (not familiar with grenade terminology), would be made with styrene pieces.
That's how I would do it, but other members here might have some better ideas.
Electronics? Have no idea. I would need to know what it does in "real" life and then see if anybody is making something similar on Etsy or Ebay.
TazMan2000