Here are some links to my online stores stocking pyrite ammonites. They are all found on Charmouth beach, Stonebarrow on the Jurassic coast.
Jurassic_coast_ammonites - eBay.
Here you will find a selection of pyrite ammonites both on offer in auctions and buy it now.
Ammonitefossil - Etsy shop
A selection of pyrite ammonites with hole drilling options for jewellery.
If you are looking for something which is not listed then do get in contact - I may be able to help.