There is no real URL for the iOS app store. Its technically limtied to iOS devices.
You can however browse here: App Store Downloads on iTunes but its not the complete app store and there is no search feature there for it. Only Category filters.
You can if you really want to, use Google or other search engine, and preface the search with the word "itunes" and something you wish to look for. For example "itunes drawing apps" and it should come back with at least the first few results from the iOS app store.
On google you can even limit it to the app store specifically by specifying the apps store's url: itunes drawing apps site:apps.apple.com - Google.com
It should produce some relevant results.