I wonder if one of those hobby jets would work. Seems like there's a lot of activity in the small jet engine segment in recent years from the likes of Kratos.
He's planning for an F15 engine, which is another class entirely. If new, it's either the F100-PW-220/220E or the F100-PW-229. It has has a thrust of 17,800 lbf (79 kN) dry, or 29,160 lbf (129.7 kN) with afterburner. If he got the old F100-PW-100 it would be 23,930 lbf (106.4 kN).