How to replace old exhaust fans in bathroom and kitchen?

[joejoeinc]

I have 2x old Mistral wall exhaust fans that have a 300 mm x 300 mm shroud going through a 220 x 230mm hole to the outside of my home. I can only find 150mm exhaust fans at bunnings. Both these fans died a long time ago (they just rattle whenever you turn them on) They really need to be replaced.

I'm looking for advice as to what my options are? should I attempt to fill in the internal wall holes to make it a 150mm hole or should I try to source a like-for-like replacement? 

It looks like this product wouldn't even cover the massive hole that was made in the wall to accommodate these older fans. 
https://www.bunnings.com.au/blauberg-150mm-white-aero-wall-ceiling-exhaust-fan_p4420505

Here are some photos that show the issue I am dealing with.   

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[CSParnell]

Looks fantastic 

[joejoeinc]

@Alison2  I've seemed to misplaced your contact details. can you PM them through again?