It's in the datasheet. Each model comes with probes that are specified at the same bandwidth as the scope.
Which brings up a good question. Theoretically, if you have a scope with 70MHz BW and probes with 70MHz BW, then you actually have a system that is: BW = 1/SQR((1/70)^2 + (1/70)^2) = 50MHz
So, do manufacturers supply a system (scope + probes) that gives the published BW for the scope? i.e. will a 70MHz scope with it's 70MHz probes give a 70MHz system?
According to the theory you would need about a 100MHz scope and ~100MHz probes to get a combined 70MHz system.