IF you dont know the HMC name for an lpar you have to search the RSCT log files.
find /var/ct -type file -exec grep -i HscHostName {} /dev/null \;
example output..
/var/ct/567237452/log/mc/IBM.CSMAgentRM/trace:Slot info is [HscName=7315C01*0215BCA;HscIPAddr=10.15.79.137;HscHostName=aig2mc601.infra.boulder.mebs.ihost.com;RMCKey=xxxxxxxxxxxxxxxx;RMCKeyLength=8;HmcStat=1;]
find /var/ct -type file -exec grep -i HscHostName {} /dev/null \;
example output..
/var/ct/567237452/log/mc/IBM.CSMAgentRM/trace:Slot info is [HscName=7315C01*0215BCA;HscIPAddr=10.15.79.137;HscHostName=aig2mc601.infra.boulder.mebs.ihost.com;RMCKey=xxxxxxxxxxxxxxxx;RMCKeyLength=8;HmcStat=1;]