You don't need a new carbide bit. You need a diamond file to sharpen yours.
www.mcmaster.com p/n 8168a13 coarse $19.22
or call 562-692-5911
you might want to pick up a couple of bits too.
p/n 3367a121 $3.42
You will need the file to put a tip on the bit, they come with the correct angles but the tip is rounded.