There are a couple of ways to get the url for your Windows 8 Store app. One of the easiest ways to look in the email account tied to your Windows Store account with the title “Windows Store: your app is in the Windows Store!”. In that email will be the link to your app in the store. Additionally, you can log into the WIndows Store at http://dev.windows.com and along the top navigation bar click on Dashboard.
Scroll as need until you see your apps in the store. Click on the details for your app.
Scroll down until you see the section that says “Link to <YOUR APP OR GAME NAME>. See the example below where the link to the app is listed..