One option is to check third-party software marketplaces or reseller websites that may still have copies of the software available for purchase. You can also try searching for the software on websites that offer downloads of older versions of software, but be careful as downloading software from unofficial sources can be risky and may potentially harm your computer.
Another option is to upgrade to a more recent version of Fusion, as newer versions often include updated features and bug fixes. Blackmagic Design offers a free version of Fusion, called Fusion 17, which can be downloaded from their website.
If you are still unable to find a suitable solution, you may want to consider reaching out to Blackmagic Design support for further assistance.