Is there an ASIN API for UPC?

Not sure why this question went through six months and got over 120 views unanswered, but hopefully this helps:

According to: http://docs.aws.amazon.com/AWSECommerceService/2011-08-01/DG/RG_ItemAttributes.html

UPC appears as one of the possible element attributes that can be returned from a request. As is the UPCList (which will contain multiple UPCListElement objects) for elements containing more than one corresponding UPC.

It says:

The ItemAttributes response group returns a potentially large number of attributes describing the item. For example, an item in the camera and photo search index might return attributes, height, width, weight, title, UPC, price, production, zoom factor, megapixel count, and carrying case.

All search indexes can return all attributes of an element. However, the number of element attributes returned depends on the ASIN. Typically, ASINs in the same search index will return the same element attributes. For example, you would expect the item attributes returned for an item in the Books search index to be different from the attributes returned for an item in the Camera and Photo search index. However, all elements in the same search index do not necessarily return the same attributes. For this reason, it is impossible to predict exactly which element attributes will be returned in the response.

Which for your question means they won't have a UPC for every item in their database, so it won't return one for everything - only for items that have an applicable UPC. And you need to make sure you are using the applicable response group - you can check the response groups in your docs to make sure the group you are using includes the UPC.

I'm just starting a project that will involve this UPC hijacking process, but haven't gotten around to implementing it yet, so the only help I can give right now is what I see in the docs.