Here’s how to replace the switches:
https://www.youtube.com/watch?v=AejWF6rNWes
Take photos of each stage as you tear the mouse down. Give your self lots of time and don’t rush. Take frequent breaks if you start getting stressed. If you relax it is fun fixing things.
Where to get the switches? I don’t know but the switches will have their part numbers on them. Do a search. One of the suppliers in China will probably have them.