I examined the situation and the old link is still accessible it's just not visible anymore.
Here it is:
This will download the MT4 Installer.
Ok i just tried it and it does indeed install mt5
That is just an unfounded excuse! If they are profitable indicators, then you have more than enough to hire someone to make MT5 versions for you.
If however, they are not making you any profit with, then it is time to dump them anyway.
Besides, MT4 is still very much alive and available at the Brokers and those will not be changing that any time soon!
EDIT: After reading Alain's post below, I just realised my "ignorance"! @johmus. Just download MT4 from your Broker!
Problem is that on 5 versions tested from different providers, they contains malware. Try uploading terminal.exe to virustotal.exe and see the results.