You can find a replacement most likely right in your home town hardware store
They have the little drawers with all the nuts and bolts and things...
that's where they have knobs. Most of these all have a standard shaft size but make sure to measure the shaft that you are using the pliers on.
Then look through the knobs and match one up.
Euro-Pro does not sell parts for the toaster oven and this is the way to go to replace the knob.
Ask one of the sales people to help you locate the right drawers to find the knobs
Here is one online at Amazon for the standard 1/4" shaft