Do all the magnets have the same magnetization. Well maybe you could use superposition and add all the little B fields together based on distance from a point.
And maybe you could also get an idea of the B field of the little magnet by placing one on a balance and seeing how much weight you had to place on the other end to pull the magnet off a piece of iron or something . Or put the magnet on a spring scale and see how much tension it tool to pull the magnet off a piece of iron and then compare this to the B field of the bigger magnet . The force should be proportional to the fields.
And you might be able to drop your magnets through a wire loop and then measure the voltage
they produce. as the emf is the change in magnetic flux .