Call junk yards looking for cats. I see some on eBay. Try Craigslist. Next best would be to source online. Aftermarket cats are an option, get a good exhaust guy to weld them in.

You're sure the cats are bad?

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2002 X5 4.6is - Titanium Silver / Black Alcantara - Dinan Stage 2 - Bilstein/Eibach - Brembo BBK ----SOLD---
1993 318i - Brilliantrot / Tan - bone stock daily driver