update for anyone in the future with the same problem.
I found a supplier in the UK who seem to have the “legit” Mellet brand CHRA
https://www.turborebuild.co.uk/webshop/prod_6487569-Genuine-Melett-UK-Turbo-CHRA-Alfa-Romeo-Giulietta-18P-53049700090-K04.html$340 shipped to SA, took 4 days to arrive. Really simple job to swap it out, the hardest part was getting the whole turbo and manifold in and out of the pokey little engine bay.
Manifold gasket from Vlade Kuga at Arese Spares in Sydney
Pulling the turbo was easy enough, I took photos and notes as I went to make sure all the vacuum lines etc go back in the right places.
Putting it back together is a simple reverse of taking it off. Important to prime the oil feed pipe when installing so the new turbo doesn’t start running dry.
I also pulled all of the intake pipes and cleaned them thoroughly and pulled the intercooler off and flushed it with degreaser and then metho. There was a lot of oil in there from the turbo’s leaky demise.
Replaced all the silly single use hose clamps with regular ones from the local parts shop. Much better seal on the ambient/low pressure side now than the wobbly factory clamps.
Changed the engine oil (possible cause of the turbo failure was diluted oil as it had been around 16,000km since the last service, oops)
Turned the engine over without starting a few times and let it sit in between to get the new oil flowing through the new turbo, then started her up and let it idle.
A few seconds of smoky exhaust gave me a heart attack but it came good.
It’s been a few days of driving now and she’s back to her old self.
The turbo must have been on its way out for a while because I had forgotten what it’s like to be pushed back into my seat with every gear change.
Really glad to have it back on the road and all up cost me less than $500 in parts, compared to more like $5k alfa would have charged to replace the whole turbo and manifold