Some of the weather proof CEM multimeters are also supplied with the jack caps probably to maintain their IP?? rating but I've never seen them available separately.. You could easily turn some up on a lathe or spit a few out on a 3D printer if you happen to know somebody with these machines. There are plenty of other options as well, for instance the plastic 4mm PCB stand-offs are a nice fit, work a treat and no big deal if they get lost.