Warlord/Italeri do an M3 Stuart/Honey in plastic. It's pretty good if you want an early vehicle (3 hull machine guns, not 2), although the tracks are a bit fiddly compared to Rubicon's M5A1 tracks. It doesn't build an accurate M3A1 though - the rear hull is wrong. Anyway, there's not much incentive for Rubicon to do the same vehicle.