Where can you download the Plastic SCM java client? It does not appear to be in the binary archives.
The archives at https://www.plasticscm.com/download/ do not have the client.
Yes, the java client is available for HP-UX, Solaris and other Unix flavors where Mono is not natively present. For almost all Linux distros, Mac and even BSD's you can use Mono + Plastic and get native performance. Remember we also launched a native GUI for Linux (GTK based) and Mac (Cocoa based).
Please contact support at codicesoftware dot com in order to request the Java client :)