Spur is very strong, as long as your heavy item is not on a shelf near the top (because leverage)
I have an idea they make 450mm brackets. You can usually put on a deeper shelf, assuming the weight will not be on the front edge.
HOWEVER
A CRT television has an armour glass front screen to protect you in case of implosion, and this is the heaviest part (hence you always carry them with the screen against your body.
The original Spur shelving company went bust, somebody bought the warehouse stock, you may be able to find them on Google. But they, or something similar, are now being manufactured again.
The original, double-wall, double-hook brackets are stronger than single ones.
As a CRT TV is very heavy, it needs to be on its own sturdy shelf and brackets, not balanced on a flimsy cabinet.