A mouse wrecked havoc on my stove insulation, what is the easiest way to get to insulation?

What kind of insulation, and what kind of stove?
Do you mean the gasket on an oven? Order on eBay, by searching on 'oven gasket' and your make of range.

Frigidaire stove insulation

Extremely hard to do. You can pull the oven, remove the case and then reinsulate and recase and reinstall. Why not get a new oven?

A stove is a combined unit with burners on top and an OVEN underneath. Do you mean that, or a wall oven?
As someone who has had to deal with mice, a fact of life in rural areas, I wouldn't spend money on a new appliance knowing it will just get torn up again.