That sort of cable is generally specialist supply, comes from suppliers that sell to switchboard and motor control centre builders. Sometimes you can buy 50sqmm or 70sqmm from welding supply shops in double insulated 0.6/1kV but ignore the current ratings on them as those are for welding cable. Brands like Aflex, Siemens, Varolex etc. Locally to me it is Hunter Engineering Sales or sometimes Bambach (who have now closed locally). There will be someone in Perth that sells it, L&H will be able to order it for you. You'd only need 35sqmm though, but you do need proper lugs and compression tool.
You do have it running along the floor uncontrolled and unprotected though. For my car I'd rather see that under the car, where exposed inside thick heater hose held by refrigerant line straps or similar, like those in the link below. I've bought them in bulk before locally:
N10236603 - Volkswagen A/c refrigerant line clamp | Carter Volkswagen, Seattle WA (cartervw.com)