I guess getting the nutmeg essential oil already and doing fractioned distillation under reduced pressure would be the way to go. Extracting with a solvent directly from ground nutmeg won't give you an adequately pure product I think.
I believe that shulgin wrote about the isolation of myristicin in the pihkal entry of MMDA.. anyway, do you have experience with lab work? This isn't something to do unprepared.
Fractional Vacuum Distallation is the only way to go for pure myristicin from nutmeg oil.
If the only desire is to consume the purified myrsticin then I say don't worry about it. Research seems to indicate pure myristicin doesn't have the same effects as nutmeg/nutmeg oil... It sounds like straight nutmeg oil is the way to go.