I am trying to rehab an older model 3 speed sturmey archer bicycle but the chain keeps breaking. Is this a special chain, for example is the linkage metric. Could I go to a local USA bike shop and get a replacement chain? I've tried an Internet search but just keep getting sites for the indicator chain.
I think what you want is a 1/8" width chain for single speed. (Here 'single speed' meaning that there is just one cog in the back.) Trying to put a multi-speed chain (which is a little narrower) on this could bind up and break. Beyond that, nothing special. Most chain breaks are caused by improper joining of the chain, so that just comes down to proper technique to avoid bent plates or a pin that isn't seated right.
Also make sure the chain is not too tight. There needs to still be a small amount of deflection available at the tightest point in the rotation of the cranks.