I think the last two flyers were N1430Z and N896U - both based in the US - and I was fortunate to see the former fly in the late 1980s while on its annual contract in support of the summer firefighting effort at Fort Wainwright, Alaska.
I subsequently saw it retired to a small outdoor museum at Fox Field in Lancaster, California where it continues to moulder away. A recent pic. is here:
http://www.airliners.net/open.file/564602/L/
N896U is at the Yankee Air Museum in Willow Run, Detroit. The museum hangar burned to the ground last month but all outdoor exhibits, including the Argosy, survived. Pic. here:
http://www.airliners.net/open.file/241925/L/
A few Argosies survive in museums in the UK.
A census of worldwide survivors is here:
http://www.oldprops.f9.co.uk/Argosy.htm