Upgrade to Mojave

I need to upgrade my computer from Sierra to Mojave (I can't use Catalina as some of my software is not compatible) when i follow the link from the apple support page on how to upgrade to Mojave it takes me to iTunes and i get a message saying it doesn't exist. If i force the link to the App Store app it similarly goes nowhere. Where can i download an installer for Mojave?

Thanks

Jason