As part of EB Games 'Christmas Sale', you could either get a full set for $98 at:
https://ebgames.com.au/nintendo-switch-225675-Nintendo-Switc…
Or, you could purchase the two controllers separately for $94 altogether.
https://ebgames.com.au/nintendo-switch-225674-Nintendo-Switc…
https://ebgames.com.au/nintendo-switch-225673-Nintendo-Switc…
Ordinary prices are $120, so if you're looking for another pair of joy-cons, these should be good.
ALSO, if you're looking for other colours instead, you can price-match with other stores such as:
https://www.bigw.com.au/product/nintendo-switch-joy-con-pair… (For Green/Pink) - $99
https://www.target.com.au/p/nintendo-switch-2-pack-joy-con-c… (For Blue/Red) - $99
Why would you only want one half of the controller? Are there 3 player games? (Genuinely curious)