Years ago I picked up a universal replacement antenna with lots of threaded adapters, one of which fit the i-MiEV. IIRC, it was under $10 at my local auto parts store. Just looked on eBay and Amazon and there are some there. I once tried to put on a longer one to improve FM reception, but it was too long for the height of my garage door.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV