You may also want to check some of the Gen watch forums like Timezone or Watchnet.
Tourneau is a Patek dealer so they can assist as well, but I prefer to support my local AD's over Tourneau.
I would be highly concerned buying a Gen PP strap from Ebay unless it was from a well known and verifiable source with amazing references, but there may be good deals to be had there if you know what you are looking for.
Good Luck