Hi,
whether it can be ground flat is really determined by its length. There are plenty of surface grinders around but they start thinning out as the length goes up.
I'll bet there three or four in your area that can do 500mm length but may be only one that can do 1m. To my knowledge there is only one in the whole of New Zealand
than can do 4m.

The good news is that surface grinding is an easy task assuming you can find the right machine. Secondly if you get SHS it is typically pretty damned good anyway, seldom
would you have to remove 0.1mm to get it flat.

Craig