WebStore is a separate feature designed to work in the context of a cms page. ie you have to add an instance of webstore to a page then webstore exposes its own admin links. it cannot work any other way and making new links to it from the admin menu is pointless.

The example link you posted would not work because:

1. resourceKey cannot have any spaces, you example indicates that there should be a file named /App_GlobalResources/MyResource.resx which probably does not exist but if it did exist resx files can never have spaces in the key

So that is most likely why the link does not appear. You may also see an error about it in the mojoportal log.

2. If you were successful in adding the link, the link would not work because the url ~/WebStore/ProductDetail.aspx expects parameters including the pageid, moduleid and productguid, without those params you will get access denied.

Actually when you create a product in webstore a friendly url will be created like /your-product-name-product and that friendly url will map to the real url /WebStore/ProductDetail.aspx?pageid=x&mid=y&product=z

so the url /WebStore/ProductDetail.aspx is generally never seen by users, instead they see the friendly url

​To use webstore first create a page to put it on then click edit this page, then add webstore to the page. After that click the administration link near the title of the webstore instance. From there you can create new products and offers. Note that first you create the product then you create the offer and add the product to the offer. The offer is where you set the price.