Hi @andy.pritchard,
We replaced the OS X installers with the OS X VMs several months ago as you can see in the changelog file
Version 1.9.18-1 2018-11-28
* Added support for OS X VM
* Updated Apache to 2.4.37
https://bitnami.com/stack/testlink/changelog.txt
They allow the users to launch the solutions and manage them in a really easy way. Those OS X VMs are specifically built for OS X environments.
Let us know if you have any questions when using it.
Thanks