You first need to figure out what choke tubes you gun takes, Mobil chokes or optima chokes are the choices. Then decide what kind of tubes you want, factory or one of the many made by aftermarket manufacturers, at that point you will know better where to look.
Teague tubes are very good, made in the UK but ship to Canada, Briley are a very good USA made brand, not sure if they're still shipping here or not. Muller is another good USA brand that can often be found locally. Factory tubes and others such as Carlsons can often be found at retailers such as Cabelas.