My nose is out of joint already, so no worries.
One way would be to look for brand names or years. That will limit the results to frames and complete bikes.
Personally I put "complete bike" in the topic title to make it easier, but many here don't because it limits their target audience.
The problem with a separate section would be that many sellers do consider splitting the bike if people are interested in the parts. If a seller decides to split, it would mean the topic needs to be moved.
Considering the amount of trading that goes on here and the rising interest in the 98+ bikes, I'm afraid that moving topics would become a part-time job over time.
Still, any reasonable suggestion is worth considering. I'm pretty sure the head admin will read this as well, and it's his call after all.