I found myself at Korber Models website today and while browsing their building kit offerings, noticed that they offer a Quonset hut that will be of use when I get around to building Motor Parts Distributors -- it has a double Quonset hut at the top of the property next to Terrace St.
Some of the detail parts that they offer might also come in handy -- the steel storage tanks and possibly the rooftop water tanks would fit on some of the Fairgrounds Branch buildings.
I didn't just happen to find this site -- I followed it through an advertiser link in the O Scale Resource online magazine that was just released today. It's free, so if you are into O scale, you have no reason not to subscribe. Or, for that matter, since it is free, follow along anyway and learn some techniques or information that will likely apply to your chosen scale.