Some Magna models came with chrome side window trim and others with black.

I think my TF would look better with black (the car colour is Frontier Green and I've removed badges etc. for a sporty look – the chrome trim stands out too obviously).

Is matt vinyl tape the best solution? If so, what's a good Aussie supplier? Any other suggestions?

You can just swap them over with the black ones.
When I had my 3rd gen I swapped to chrome. Tj comes stock with black.