Bromax-You can drill your rims to Schrader valve sized holes,that way you can use either type tube.There are little adapters for using Presta valves in the bigger holes,but you can just build up the Presta valve a bit by wrapping it with strips of duct tape so it doesn't wiggle around in the now enlarged holes.
It is still easier to find a Shrader valved 27" tube at Walmart and sporting goods stores than a Presta valved tube.Luck,Charlie
PS I remember when I 1st saw a Presta valve in a bike store about 36 years ago-I was a bit puzzled-WTF is this????