Not as a specific dynamic forum, no. From experience, I've found that whilst there are some generous souls happy to share sounds, the vast majority either a) just want to take sounds and / or b) want to keep their own sounds to themselves.
But there are these;
There is here - you can upload attachments; you could start a sharing thread and see if there's any uptake.
There is the FB Jupiter 80 page - again you can upload attachments and hopefully start an active sharing activity.
There is my site http://www.JP-80.com
, which does have some sounds (and other very useful files) but it's not dynamic - sounds would have to be sent to me for uploading to my server.
So those are the three options that are out there now. You could of course start your own website focussed on sharing sounds for the JP-80 :)