There's gotta be something you can use in place of that.. its just a check valve after all. I bet Audi's would have something like that

 

Turns out, it's only sold with the hose and spray end and spring attached.
Part — AWR2406
Getting one from Rimmer Bros ('cause they didn't want three times it's price to ship it).

 

Following up, just because.
Got the (genuine) Land Rover part that has the hose and spring.
Turns out the hose in it is about a full 10 inches too short (see photo - new part in the foreground). Everywhere seems to agree it's the right part. So no idea what is going on there.
So I did end up having to use the original hose.
Which wasn't the worst as I haven't a clue how you could pull that spring off without snapping some part of the plastic arm. Maybe there's a trick I don't know.
I think I'd recommend just getting a generic check valve from Aliexpress and waiting the 8 weeks.
A surprisingly expensive and frustrating experience all round.