GK,
Over the years I've replaced broken mag springs in a few different makes of rifle by modifying Ruger M77 springs.
Because Ruger makes a specific .308 length action, maybe one of those might be adaptable to your BRNO.

Here is a clue regarding breaking mag springs.
When ever you need to alter the bends, never try to change the angle of the tight bends in the spring. If you do there is a high chance of breakage.
Always do any bending at the curves in the limbs of the spring and you shouldn't have breakages.
I found this out the hard way many years ago when I broke a mag spring in a 50's BSA .308 featherweight, and of course there was little chance of finding an original replacement.
Some minor alterations to a Ruger 77 short action mag spring had the BSA back in action in no time.

I don't know if one will work in your BRNO but it might be worth checking out.
Hope you get it working again soon.