100-150 hours a year would barely justify ownership of a much smaller plane, let alone a Gulfstream. And, for only once a year overseas, you really don't need that large longer-range plane for every trip. From a business sense, the numbers would simply never make sense.
And, what everyone else said, older airframes can be problematic.
Fractional operations are an ideal fit for your planned mission profile, and depending on what program you were in, might even allow a selection of appropriate aircraft better fitted to suit each trip. I'd suggest contacting several fractional outfits during your research.