Thanks for the link wingwalker123.
The thing is, I was after a jack (so a 'female') not a plug ('male') as I'm converting from GA to XLR5 (not XLR5 to GA). Thanks anyway.
I have now found one in the US and have soldered a converter plug and it works a treat (on a Boeing 737-800NG).
If anybody is looking for the same thing, please contact me.