Hi Jack,
I apologize that the retirement of M-Lab site LHR05 is causing problems with your production environment. Unfortunately, the circuit for LHR05 was turned down by Lumen, along with the IPv4 prefix that went with it. We haven't generally attempted to announce when new sites will be turned up or older sites turned down, because the expectation has largely been that all integrations should be using the M-Lab Locate Service to get a list of nearby, healthy machines to test against. You really shouldn't need statically configured fall-back addresses to test against, as the Locate Service should be highly available. Have you found that it isn't?
Detailed information about every M-Lab machine is publicly available:
There are various other more abbreviated formats of the same data:
This may not be possible in your case, at least in the short term, but I would recommend against configuring a new set of static IP addresses to test against, and instead put the engineering effort into relying 100% on the Locate Service (different from "mlab-ns"):
There is considerable churn of M-Lab's physical infrastructure at the moment, and you may very well statically configure new addresses that will themselves go away.
Best,
Nathan