Flightpath do sets for bothe the Harrier GR3 and the Sea Harrier FRS 1, they are very nice sets but I hope you like Photo etch, as almost everytning in them is brass. Unfortunately this extends to things that would be better cast in resin. However, you can't go far wrong with them.
Heritage Aviation also have detail sets in resin for the Harriers, I hae both the Heritage and the Flightpath sets for the FRS1 and between the two a very nice model can be made.