The Sword Buyers Guide is probably the remaining forum where some of the long term modern collectors still gather. All Swords and the IASC rooms on Facebook.
https://sbg-sword-forum.forums.net/
https://www.facebook.com/groups/iascpost/
https://www.facebook.com/groups/1243498752490849/
There are other FB groups but those stand out, as visible
Cheers
GC