A spring problem

[dalisprime]

Hi guys,

I've come across a minor nagging issue with my rts Lugnut - the 'punch of kill everything' on his left hand didn't really work properly and when transforming to plane mode the wing tip did not snap all the way to the wing leaving a gap. Grabbed my screwdriver to see what's going on in there and found the culprit in the form of multiple twists/bends/deformations (whatever you call them) on the spring that powers the whole mechanism.
This is where I turn to you - any suggestions where to get a spring I could use as replacement? It's probably something trivial (not pens though - tried one and it was too wide) but my brain is failing me for the time being

Cheers in advance