You should redue the whole lower end of the rod if it's a two piece. You can at times replace the lower end with cork. But the problem is that the cork from boring it out will be to thin.
If you do decide to replace the lower end be vary careful when removing the reel seat, so the you don't crack the blank.
Anglers Workshop in Woodland as your best selection as far as parts. Their phone number is 360-255-9445, or check out their web site at
www.anglersworksop.com
If your driving north on I-5 at Woodland they are right along the highway on your left.
Good people to deal with. They use to be one of my wholesale companies when I was building rods.