Hi Joseph,
The SciJava Maven repository's public group is a collection of other repository proxies. Regarding the two artifacts you cite:
This one is available from Icy and Jitpack.
This one only from Jitpack.
And Jitpack is a unique repository, in that it builds artifacts on demand the first time they are requested. So the requests can take minutes to complete, sometimes timing out. It's not a great approach IMHO...
Why are you trying to access these artifacts specifically? And which "many more" are you referring to? Please tell me you aren't mirroring the entire SciJava Maven repository index...
Regards,
Curtis