...or E-Bay:
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...says it 'can improve the sound quality of transmission'
Make sure you select the correct one in the pull-down box, as they do 4 different types.
When I Iooked, the one you want was one of the only two they had in stock, £11.82.
Although you may be better off going for one of those with a cable - otherwise, with the above type, once you go into an additional 6.35 to 3.5mm adaptor, it's starting to get silly (too much leverage waiting to break the plug off).
To do what you're after, I just bunged one of these onto the end of a TRS cut-off 3-core cable:
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