Not sure if anyone here is aware of the active group on Facebook.
Even though it's titled "Hupmobile Australia & New Zealand Register" it's for Hupp enthusiasts world-wide.
They produce an excellent newsletter only available to members and by post. There are many members from the USA, Europe and Great Britain.
Just do a Facebook search for Hupmobile Register - Australia & New Zealand and join on their page.
https://www.facebook.com/groups/342222776149425/