HP 82168A Acoustic Coupler, HP41 books

[Noelene]

Thanks for adding me to this forum. My husband passed away recently, and I am sorting through his large collection of HP calculator equipment in order to sell it off.
First, are there many on this forum in Australia, where I am (near Canberra, ACT)?
Secondly, I came across an 82168A Acoustic Coupler - it seems an unusual article, would it be valuable?    
Thirdly, I am sorting out the calculators with their manuals and accessories so I know what I have, but there are several separate books on the HP41 (HP-41 Extended Functions Made Easy, HP-41 M Code for Beginners, HP41 Synthetic Programming Made Easy). Would it be better to offer these for sale here where members might be interested in these, than on eBay?