O scale in trains is 1:48 … so your trains would probably be a bit out of scale compared to the tanks and vehicles.
A quick google didn’t show a lot of product in that scale though and I noticed that Marklin only does H0 (1:87) scale at best.
I suspect the tiny trains are easier to sell given the small footprint.

OTOH .. it’s not like wargame manufacturers actually care about scale, with the possible exception of the 1:56 scale Italeri tanks that Warlord sells.
Don’t expect it to be cheap.

O scale can be 3 different sizes depending where you live in the world. S scale as @sundancer says will be the closest.  Sadly 1/56 railway modelling wise just isn’t a thing.

I hate saying it but do you know anyone with a 3D printer?

Some of the MDF manufacturers do railway gubbins in wargame scales. The scale is closer but at the cost of detail. Personally I’d be more inclined to use O gauge stuff.

@sundancer common scales for models are 1:35 – 1:48 – : 1:72 (and for some reason 1:76). There are more, but they’re usually for things like ships and airplanes which would be too big (and expensive).

The 1:56 is unique to wargames and possibly toys as far as I know.
I think Revell has an X-wing in 1:56-ish scale and I think that air speeder is similar, but that stuff is kind of non standard for whatever reason that I can’t understand.

https://wargamesandrailroads.blogspot.com/2013/04/s-scale-vs-on30-for-calamity.html

I’d prefer the O scale over the S scale mentioned in that article to be honest … but it will depend on what minis you do have.
Big chunky ‘heroic’ scale minis won’t look bad against O scale, but they’d look ridiculous next to the S scale train.