Help needed for my JDM V7 STI rear diff
 

Good evening, I'm in need of some help regarding my Bugeye. Ive only been told from Buying it that it has a Cusco rear differential but it's binding, it's been binding for a fair while but assumed it was just because it had a naughty diff. But the front judders when turning and I've had someone to look at it.
so I'm in need of a new one and the one I need is a R180 3.9 ratio from a JDM V7 STI. Need some help on that so asking of anyone has one to sell or know of any being sold.
Or a reputable company that can fix the one I have if it can. It's incredibly annoying and something I need advice on.
Thanks for reading