Your best option is probably going to be in contacting Corsair first of all.
While they may not provide one, it's worth trying - especially if you still have proof of purchase.
I don't believe they're sold stand-alone.... but most of the Corsairs mounting kits should be interchangeable, so if one is available via them, you should be fine.
You could also look to eBay etc.
For example, a damaged cooler (never used, damaged in the box) would have all the required mounting...... bidding is currently <$20.
https://www.ebay.com/itm/Corsair-Hydro-Series-H100i-V2-Extreme-Performance-CPU-Cooler-READ/273270318195?hash=item3fa02e2473:g:-zUAAOSwFOZbGgTt