Hi Nick! these manufactures make it REALLY hard to buy component level replacement parts, as youve found out im sure.
i think your best bet would be trying to find a donor mouse to pull from
something like this
https://www.ebay.com/itm/Razer-Naga-Trinity-Gaming-mouse-Motherboard-with-scroll-wheel-RZ01-0241mainboard/293916471124?hash=item446ec96f54:g:XKYAAOSwrptf4UtB
good luck !