Adjustable collar ties

My daughter's house as a problem with the walls spreading apart due to the weight of the solar hot water system on the roof.
I have checked in the roof space and there are no collar ties in that section of the pitched roof.
I don't think that this can be easily reversed, but what I am proposing to do is fit some steel adjustable collar ties and wind them up as tight as possible, and hopefully this would stop the problem from getting any worse. As there are no internal walls in this area to support the roof, my idea seems to be the only reasonable fix.
My problem is that I have been unable to source these adjustable collar ties.
Is anyone able to advise where they might be available in Perth.
Thanks in advance


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