never let it be said….
I followed up my own post.
Yes, they or equivalents do exist.
"Starlock" is one make, according to Intafast.com who also show a simpler, more generic "push-on fastener" with no trade-mark name.
You might find them stocked by motor-factors (probably in a snazzy compartment-box of oodles of several sizes!), or you could try a domestic-appliance repairer happy to sell you just a few of suitable size.
Model-Fixings might stock them too: worth asking. Among "our" suppliers, and I have used them a few times for small metric screws and nuts.
'
For more specialist parts like the pump leather and valves, you could try BaseCamp, in Brighton. They specialise in spares for oil-lamps and the like.