It is very easy to swap out a switch. As in the link Dranno posted it is pretty much step by step. I only changed out the single switch that was giving me trouble instead of pulling the whole 8-way switch out. Yes the analog switch are the same, so having an old analog CH stick is great for parts. As for where to get parts, I think any electronic store should carry those buttons.
Check out the CH-HANGER forums for more details. You may even find someone posting a part number for the replacement button your looking for.