NeoLoad 5.0 and older are not compliant with MacOS. That's why you can't find any installer for that OS. The next version of NeoLoad will support MacOS.

However, you can still currently use the Unix installer and you will have to manually install your own JRE. All the NeoLoad features won't work but it's still useable. 

I would suggest you to install the Windows version till the support of MacOS is available.