I guess it's just the way the parts sites are layed out or something, I needed an engine part for my bike and couldn't find it, my dad found it under the same year but a different model bike with the same engine.
But if it were mine, I'd just go ahead and get the gasket for it. But, on the other hand, if it was running fine without it why put it on there. It's up to you really, but I personally would put it on there
Wrapped RPW Slash pipes
K&N air filter