What ya need, Allan?
Unlike down under we have many useful calibers in the home!
What you need? 30:06 (7.62 NATO), .223 (5.56 NATO) or something like a 30:30, 45-70 or the like?
I kill 3 or 4 deer a year with my .44 Magnum sidearm they are about roo size. Need to get a bit closer with the pistola tho.
I could loan you an effective weapon for that size beastie but not sure how the authorities would react to that?
Hehe, might try snaring them.
Just some cable and a drag about their weight.
A self locking slide is easy to make from a washer with a cable sized hole on one side.
Probably illegal but very effective on raccoons, badgers and coyotes or nuisance deer.

Tom