Ebay comes to mind. If you can't find what you want there you could consider getting new controls and auctioning what you have to help absorb some of th cost of the new controls.
You can always try taking your brake arm to a place that does machining and having them cut off the pedal, finihsing the end off nicely, then boring and tapping a hole for you to insert your peg. Wicked Image does custom bike works, making wheels, shifters, etc. They probably wouldn't have a problem running of a piece to match what you have.
See what the manufacturer of your controls says. If it's something from, say, Kuryakyn or PM or whomever, they might have what you need and be willing to part with just the arm and not the whole control.
Converting to brake peg. 
Linear Mode
