With a bit of care you could 'mould' your own grommets with a bit of ingenuity and woodwork skills (perspex perhaps?) and an applicator gun tube of Sikaflex 521 or similar polyurethane car body sealant/adhesive.
Make 4 no. oversized timber or perspex disc's, say 3/16" thick - (two these will be outer parts of your mould) and should be drilled for a tight but removeable fit of the respective breather tube or PCV valve.
The two (inner) disc parts of your mould need to be drilled/turned-out to the maximum diameter required for your grommet. Say, 2" or 2 1/2" diameter for a 3/4" or 1" breather/PCV. These two disc's are the inner moulds for the inside and outside part of your grommet mould.
The inner and outer rocker pairs of disc's need to be secured tightly together (so glue, staples, short nails, whatever) to avoid the Sikaflex leaking out. A small hole should be drilled in the outer disc to match the size tip of the Sikaflex applicator.
Degrease and clean the rocker cover where the breather or PCV is to be fitted. Assemble the breather or PCV tube and the respective pairs of inner and outer disc's.
You'll now need to figure a way of clamping the inner and outer discs tightly to the inside and outside of the rocker cover for 20/30 minutes or so while the Sikaflex cures. Apply the applicator nozzle to the two small holes previously drilled in the inner and outer disc's and using an applicator gun pressure feed the Sikaflex in to the inner and outer moulds respectively, covering the hole with masking or duct tape. You'll most likely get some Sikaflex squeeze out........when dry simply use a sharp blade to remove any flashing. Hopefully job done..........
Could have a go at making some but hopefully will find the correct ones somewhere.
