Those are for the motor side of the carbs.
The ones Clark are referring to rarely show up on Ebay, If at all. They can be readily bought remanufactured from our German friends though.
There's also other alternatives if that option also doesn't work. Like using silicone couplings with clamps or getting creative with other materials. I've brainstormed some other hardware-store type options on my own but never got around to following through with em.
Anytime I've seen an airbox with boots included or just used boots on ebay the condition of those boots appeared to be questionable at best.
Let me know if there's any other way I can help
.