Try Autodoc: https://www.autodoc.co.uk/spares-search?keyword=AU5A-9D370-FC

The sensors on my 2005 are as follows:Upstream nearside with a grey latch plug is YL84-9F472-AE. Upstream offside with a green latch plug is IS7F-9P472-AB. Both have four wires. 2xwhite, grey and black. It is not obvious why these are different, other than the nearside needs a longer cable run. The latch plugs are the same design. Downstream of the catalysts, the sensors are the same both sides, with blue latch plugs. 2S7A9G-444BA, and again with four wires. 2xwhite, grey and black.

You will probably have to source bespoke catalysts, and I'm looking now to get one for my GDi. Some exhaust specialists will offer this service.

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4