As I'm doing my post-apoc in 1:72...any idea what scale that's close to for trains? HO? OO?
HO is 1:87 O scale is 1:48. S scale which is hard to find is 1:64. In the UK there is supposedly a OO scale that is 1:76.
There is no supposedly in it, the default scale for UK model trains is 4mm to the floor (1/76) running on 16.5mm gauge track (yes HO gauge so just over four foot gauge - in scale for the Clockwork Orange but not much else).
https://www.hattons.co.uk/stocklist/1000588/oo_gauge_1_76_scale/productsbyscaleNote for non UK readers, model railways in the UK are X Gauge, not scale (so OO gauge, N Gauge) as it is the track that is key - our nine millimetre gauge trains are 1/148 scale.
One reason is we have multiple gauges for the same scale, so if you talked about OO scale, that could be OO gauge, EM gauge (18mm gauge) or proto(Scale)Four (18.83mm).
In answer to Leadfoot's question, HO/OO will probably be the answer, depending on what look you are after.
HO/OO track is readily available, cheap plastic toy track or second hand metal and plastic should be cheap.
Dapol inherited the Kitmaster/Airfix kit range and in the UK you can probably pick some up cheap but they are UK prototypes, so it depends on what you want.