Voltech's PM3000 could connect directly to the system under test: depending on the current level you are measuring you might need to use CTs. It will measure current and voltage THD, and give you harmonic power too.
If you use an isolating transducer with good bandwidth you could use any of the numerous spectrum analysers from the usual manufacturers.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!