Are there any sources on the web with a PFM spare parts catalogue that you can recommend ?

I would be very surprised if there were. PFM parts are scarce enough that dealers are going to hold on to them for their own restorations. If you are looking for specific parts, I would recommend a WTB post, and also watching auctions for donor pens.
This is not to say that parts lots don't crop up occasionally, but these are more like "5 turning knobs" or "3 nib units" kinds of lots.
As much as I would love to know of a PFM parts supplier, I strongly recommend you obtain what you need before you share the info.

Regards, greg