Are you close to a dealer? I know the last time I walked into my Kubota dealer (3 weeks back) they had them on a shelf right in front of the parts desk.
But you need to know the size and style of the coupling. You may have to order both sides on Amazon as a set.
Summit Hydraulic also sells them online. You can get one of them for the side you lost.
If you’re wanting one in a particular color then that gets a bit more difficult in the smaller size but with your size tractor you’ll probably be 3/8 or larger