I seem to recall Oklahoma or Colorado. I recall people remember seeing him in town and he went on a ride with some people and never came back.
Not sure about any missing biker but the following organizations host rallies.
Oklahoma has an ABATE (A Brotherhood Aiming Toward Education)
website and some publications/newspapers/newsletters in a folder called "Biker Journals"
here. The 2009 issue (screenshot attached) mentions rallies that have been going on since 1999.
There's an ABATE of Colorado, that stands for A Brotherhood Active Towards Education, and it has many 'districts' according to
this webpage. You may have to dig for rally info.
What about Kansas? Does A Brotherhood Against Totalitarian Enactments (ABATE) sound familiar?
"Kansas 50th Annual National Labor Day Rally 2025 Schedule" and "See you next year for the 51st Annual ABATE of Kansas National Labor Day Rally" are written on
this ABATE Kansas website.
That means they've been hosting rallies since 1975, which is in your timeframe.
I just discovered these organizations because a
different biker went missing this year at one of their KS events and was found in OK, but I haven't found any information about a missing rider/biker from 25+ years ago. Maybe the new story about Patrick "Crim, 34, [who] disappeared after being last seen about 9:45 p.m. Aug. 30 at an ABATE motorcycle rally at Lake Perry" will jog some memories.