If you're up for trying something new (I'm not a sound Font fan) you can
get a free Mellotron gig file at
(Look under 'Oldies'.)
and run it under QSampler, the GUI for LinuxSampler.
(Build everything on Rui's LS page if you're interested in trying any of
LS is all very much development software, and there are a lot of changes
going on right now so it may be broken, but maybe you'll get lucky. LS
is a Jack application and gerneally runs very well for me on most gig
files. There are still a few it really dies on but I cannot get the
developers to pay attention to those yet.
I use a different, for money, Mellotron gig file under QSampler and GSt,
but this free one is certain OK when buried in the right mix.