I’ve been scouring the web for some icons and these are the best sites I found for SVGs (which you can turn into XAML paths).
Foreword - Segoe MDL2
If possible, consider using the Segue MDL2 font. It has plenty of great icons which scale beautifully. Here is a cheatsheet, though I don’t find it exhaustive so make sure to check our character map.
The following are my favourite sites
I would also recommend you checkout this package. It has many of the icons from Entypo and Modern UI already setup as XAML paths