I do not know the first thing about MPE and neither about the more
'exotic' code sets you mention, but I could find most of the code sets
in the iconv(1)/iconv(3C) documentation, specifically in the
/usr/lib/nls/iconv/config.iconv configuration file used by iconv(1)/
iconv(3C).
Minor nit: AFAIK, "codepage" is a ('IBM') PC-ism. The general terms
are normally "code set", "character set", "symbol set", etc..