The 4 speed toggle chain and indicator has been obsolete for many years but now they are available again. I have had some pattern sets made and these are now for sale at £35* per set.
These toggle chain sets are available in both lengths to fit all Sturmey Archer 4 speed hubs. I will need to know the length of your axle for me to supply the correct set.
I can also supply indicator sets for Sturmey Archer K, TF and ASC hubs.