Can anyone tell me where I can purchase one these in Australia or from England

This gasket is in fact a slotted 'o' ring that fits to the thermostat - it's part no is 6842214 and it's the same as used on just about every "redblock" from 240 series cars to 940s.
The 'o' ring is available seperately but is also included in a genuine thermostat.
If your Volvo dealer says "no chance" if you ask for a 360 ring - ask for one for a 1998 940 2.3lt (same item).

Certainly still available in UK - I cannot imagine them not being available in OZ (if you really get stuck report back and I'm sure we can sort you out from here.)

PS - why needed? - not known for leaks - but inlet manifold gasket can seep and give impression of thermo housing.

Mac.

just changing it.I recently picked up a 360 GLT and want to change most part that I can easily do