As of now, we don't have that yet.
99% of the vendors only provide GPL license for their items only, not their demo site or tutorial. However there's a work around on that.
To see the item demo and/or tutorial you can do a quick Google Search :
- "item name" demo
- "item name" documentation
Replace item name with the item that you want to look at.
Example the item name is ReviewPRO theme from Theme-Junkie, then you can simply do a quick Google Search with this keyword: "ReviewPRO" documentation.