Hi Briracer,
I'm only new to restoring a 500/4 but have quickly discovered that pipes for them are pretty thin on the ground but there are/have been repos done of them.
Just missed out on the last set that 'Put a 4 Parts had in Australia only a few weeks ago.
Emailed 'Dave Silver Spares' in The UK and they told me that there could be some in the new year.
Cheers.