Your search for "monarch" revealed the following:
MONARCH SPAS 210 X 145mm 50 spa filter cartridge - MS50 C45 O2 Monarch Spa Filter
There is an Australia-wide shortage of Monarch spa filters. We have been advised the importer should have them back in around 21 July. Any orders for these will be shipped directly...
SpaNet QuietFlo XS-3C Spa circulation pump 350w - Genuine & Replacements