The 4 rivets, shape of plate and type of fabric are indicative of a later type of Hardy designed coupling, many of which we used in conveyor and other drives. They were the cheapest and most common style of flexible drive coupling (usually with cast iron disc type coupling halves having 3 holes and 3 slots in each), and were available from most of the power transmission product manufacturers - Fenner, Croft etc, most of which have now gone. Have not bought one since the early 90s, but they may still be available?
However here is a company making new couplings from the original Hardy tooling - may be useful:
http://www.gmspolymer.co.uk/flexible-couplings.htm
(Well, you could spend a lifetime trawling through skips and never find a sheet of pump leather. :cool2: )