Aoshima makes a very nice 1:72 scale Dropship. You can see it at Hobbylink Japan's ssite: http://www.hlj.com/product/AOS09066
Halcyon made the original styrene one, also 1:72 scale. Tsukuda Hobby re-issued it in the late 90s. Long OOP from both makers.
Garage kit maker SMT out of Canada had a really nice 1:48 scale one in resin. Long OOP and might come up on Ebay occassionally for TONS of money.
Konami issued a series of gashapon, or "trading kits", in which the second set included a small Drop ship. Most of these gashapon models measured 4 to 5 inches or smaller. This series is also OOP.