Anyplace that sells a particular gate, should sell the manufactures extra springs as well, be it here or the US / Japan.
No idea, but they wont if they're not the correct size. They could not seat on the actuator top or hat center, or even bind on each other (if running two springs)
But those of similar dimensions (inc the gates actuator internal dimensions) will be ok.
I think your right - was tired. Id assume its 60mm, ill check again and edit in the morning
EDIT: course you cant EDIT posts over a few hours old on SAU, which is teh ghey.
Those X and Y figures need a decimal place between last and second last digit obviously