I did not see a response back from my first post, but wanted to send the following before I sign off for the night.
I asked about the TOTAL number of handsets you already have because most Panasonic Main Base Units (including this one) can have UP TO SIX (6) handsets registered at any one time. So if you already have that many registered, trying to add an extra handset wouldn't work.
I asked about if the COMPLETE systems were available LOCALLY, because trying to find JUST an extra handset can be very difficult. This is because these SYSTEMS were made a few years ago in "limited numbers", and very few of these "Wine Red" systems (and handsets) were made.
So it MAY be easier to find a complete SYSTEM, with two or more handsets, instead of a single additional handset.
Now I DID find the systems listed on both the Panasonic website and on Amazon, for about the same cost (depending on shipping). I have links below to both sites.
KX-TG6572R system on Panasonic Site >>Click Here<<
Search for KX-TG6572R on Amazon (search results) >>Click Here<<.
NOTE: I noticed that some of the Amazon results were for "refurbished" systems, so please check ALL the details about warranty and return policy if you notice that detail in the listings.
If you do decide to get a system (vs. just a handset), the extra base unit could be used as a "spare" - in case the one you have now ever has an issue, and the handsets for the new system can be "de-registered" from the new base and "registered" to the current base unit - to expand that system.
I hope this helps. Please let me know what you find or if you have any more questions.
Take Care, Greg A.