Thanks to all for your suggestions.

It really is difficult to find. I've looked at miniature train stores, but their girder bridges are quite expensive usually. I was surprised they didn't sell modular girder sections to play with, but the people at the store told me the train crowd usually build everything from scratch with plasticard girders and beams from architecture model stores.

Yes, sprue parts are the poor man's beams and girders, but the problem then becomes simply "too complicated". My forte is in creativity when it comes to designing shapes to play in (with miniatures) and which look realistic still. Not in actual technical finesse. My paintjobs are not outstanding.

This guy from the first pictures in this link has some girder supports that I haven't seen anywhere else; the post is from 2011, so probably too far back:

Mantic has this kit, which would be cool if only it wasn't so expensive (how is this small tower almost as expensive as the Basilica set?). If they sold only the girder structure in a sprue of two for 5€, I would buy 20 of them and be a happy man who has spent a 100€ on plastic casts. My dreams of industrial wasteland would be fullfilled.


Now that we're on it, another difficult thing to find:


That is, cheap objects vagely-shaped like onion domes. They sell onion domes with 80€ build-your-own-Orthodox-church kits, or even as terrain for WW1 and WW2 wargames (although too small in those cases), but they're all very expensive.

I just want shapes that can be vagely reminiscent of an onion dome. I tried Christmas tree decorations, and I know there are some that look the way I want, but haven't found them yet. My Polish-Slavic themed Imperial Guard demand a belltower.