Well for starters, Kirby pretty much spent $0.00 on advertising, there were a handful of ads from the 50's, and there are some ads for the pre-Kirby machines such as the Vacuettes and that's it.
I am a huge fan of Kirby (hello!) but as Alex noted, Kirby was sold in person and not advertised, therefore the lack of print material. I'll see what I can come up with though.