You can get through Bunnings special order https://www.bunnings.com.au/powerfit-26cc-air-filter_p0203787

But I agree with N1KKO - it is a complete rip off.

My suggestion is to run down to clark rubber and buy an off cut of foam for a few dollars. I buy 2 types - about 1/2 inch and 1 inch thick. then cut to size. Last time a just went and bought a 1x1m sheet of each and still got change out of $30 from memory. Have still got foams from 2017 still in service and not degraded at all

Please ensure you oil it.