A bit back I posted a photo of a Sheaffer sub-brand WASP-Clipper pen in pattern collectors call "circuit board" (available in a few colors with varied transparency pattern) with matching plastic pocket knife.
WASP CIRCUIT BOARD PEN WITH MATCHING KNIFE
While there have been occasional discussions regarding pocket knives that might have been issued with intent to sell with or match to pens (I have vague recollection of this perhaps being case with Wahl), there is no evidence that most of the period knives found in "pen plastic" were intended for sale with pens. I suspect it is more likely the pen makers could not keep plastics from leaking to manufacturers outside the field.
I've seen pocket knives done in stripes to match Parker's Vacumatic and Sheaffer Balance. Some colors are a perfect match to known pens; others are closely related though perhaps not identical. There is no well defined niche in the hobby for collecting items coincidentally done in matching materials. This is a separate scene from thermometer cases, holy water sprinklers, and even perfume bottles known from pen catalogues or carrying pen brand imprints. Knives done coincidentally in matching or nearly matching plastics remain curiosities, but carry charm no doubt for those who just like the plastics of the era.
They turn up on ebay, sometimes very cheaply.
In addition to the knife with WASP circuit board plastic from the link above, I just acquired one that appears to be at least closely related to Chilton's charteuse, a green-yellow with red and white veins. The knife actually leans more to green while the pen (as with most I've seen, perhaps all) leans yellow. Have most Chilton pens shifted (I've not seen pencils) a bit, or does the knife's backing of metal alter its apparent color? If neither, then the knife is a close rather than perfect match to original Chilton plastic.
Still, this makes for a nice pairing.
regards
david