New US GI replacement barrels are very scarce. If found expect to pay $4-500. Then there is the installation cost incl finish reaming. Criterion barrels makes a MILSPEC replacement but it requires both a rear and front sight base/collar. Criterion M1 Garand barrels are available in Canada, but I've never seen one of their M1903 barrels for sale. Criterion Garand barrels are good shooters and are on par with US GI replacement barrels.
Barrels can be imported from the US provided the necessary US export permit is obtained.
The majority of M1903s that I've seen over the years have needed replacement barrels due to heavy use and shooting corrosive primed military ammo.