I'm moving my Ultegra 9 spd component group over to a new frame and the front derailleur is a clamp on FD-6500 but the clamp is for a 1.25" and the new frame is 1.375". The new frame has a Shimano clamp for a braze on FD already. Can I change out the piece of the front derailleur to change it to either 1.375" or braze on? Where can I buy this? What are my options for a new front derailleur as Shimano doesn't seem to sell a 9 spd Ultegra FD anymore. Thanks

I don't think you can change your derailleur clamp. YOu might be lucky and have a larger clamp with shims in it. If that is the case, you can remove the shims inside the clamp. If you don't see the shims, then you have 2 options: buy a larger clamp-on derailleur, or buy a braze-on and use the clamp adapter that your new frame came with. For a new derailleur, you can check ebay for the correct FD-6500 part. I have used 10spd FD's on 9spd drivetrains with no issues. You could also buy a Tiagra derailleur which is currently sold in 9spd variety.

Jenson offers the Tiagra 9-speed fd in braze-on form for $39 for the double:

https://www.jensonusa.com/store/produ...ra+Fd4500.aspx

And $42 for the triple version:

https://www.jensonusa.com/store/produ...ra+Fd4503.aspx

How lucky are you generally?

Take a close look at your front derailleur. I've had some clamp-on front derailleurs that were actually braze-on derailleurs that were bolted onto a clamp-on adapter. My tandem has a 9-speed Ultegra front derailleur that came like that. If yours turns out to be the same this might be a good day to buy a lottery ticket.

I have swapped out clamps from derailleurs without problem before. Only time I had an issue was with a clamp that had been attached to derailleur with loctite so I could not remove one of the bolts. That said, FDs are pretty cheap so I would probably just get a braze on one that works with new frame.