If you can't get the correct tool, or find a friendly shop to swap the spring for you, go get yourself some heavy duty cable-ties - the 8-10mm wide ones...

A few of those compressing some of the coils will be enough to slip the collar up and allow you to remove the big circlip-type-thing holding it all together.

Only compress 3 or 4 coils with each cable-tie, and pull them tight evenly.

Andy.
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