Well, there ARE sites around where you will see such things advertised....
eg
<a href="http://www.thehanger.co.uk" target="_blank">www.thehanger.co.uk</a>
<a href="http://www.aerojumble.co.uk" target="_blank">www.aerojumble.co.uk</a>
or check out other useful links via my website <a href="http://www.lutonminor.co.uk" target="_blank">www.lutonminor.co.uk</a> (the useful links page funnily enough...)
or possibly someone here has such a thing - but buyer beware .........
Main issue could be compatibility with your nice shiny new David Clark (or whatever you've got) ..... try before you buy to make sure they work ok in the aircraft that you fly.... or get a guarantee from the seller that they'll take them back if not compatible.
Also, the weakest & expensive links are the connections to the mic jack plug - it's a specialist size & is a relative fortune to replace (£30 I think), plus mic leads and connectors often get torn and stressed because they're moved around a lot.
Example on the compatibility thing - I had (still have) 2 Softcomm headsets bought from Mendelssons over 10 years ago for £99 ea. They work fine together. And in most aircraft they will mix and match with DCs. But in a Jodel I co-owned they wouldnt - just got a screech every time either of us tried to txmit.
They're still my only headsets by the way and in my view are more comfortable than all the DCs that I've tried. DCs tend to give me a headache after about an hour, but that's just the funny shape of my head......
On balance, I'd recommend you get a new, matching headset. For the extra money, you'll get some sort of guarantee, compatibility, assurance that all the connectors and fragile bits are ok, a backup should your own one go u/s on you and your passengers will feel good wearing a "real" headset like you !