I dont know of any, but I've only owned my 1000's for a year and have lots to learn.
There is the 500mm that Graham is selling?!!!
*disclosure - I don't know Graham or have any motive to share the link below, well maybe except for you to buy the lens so I can keep my own GAS in order *
(there was a url link here which no longer exists)
I've had a M645 since 1985 and have never come across any third party lenses, and I don't believe any were made. However one or two third parties definitely did make a x2 teleconverter, but I can't remember who they were.
I think there's a Ukranian company who adapt Russian and possibly CZJ lenses for Mamiya 645 cameras, and I believe they sell an adapter for Kiev 88 & 60 lenses.
A quick search and there's quite a few adapters on Ebay to fit Pentacon Six as well as Kiev lenses to Mamiya 645's and they are inexpensice £20 ($31). These are cheaper than the Easter European ones as well. You have to stop the lenses down manually.