Identifying Legacy Spa Jets/Air Injectors

Found these very old jets in my spa.

They go iside the pipe which has corresponding notches so no way to replace them to a new type without remodelling spa completelt as it seems.

The nut is 1/2" so the overal size of the jet is small.

Any diea what are those and how to find a replacement?

Wow I accidentally founf the pagw with this part: Waterco Concrete Spa jet replacement Venturi Nozzle - Bayonet fit

But I see the stop in Australia. I wonder is this is something availablee state side.