Amazon Product API Search Unavailable Items

Currently, I am using amazonproduct to search items' UPC code based on keywords. It worked for most of the cases. However, sometimes I did find that my current search function could not find items which were not available (or sometimes it only returned a fraction of items containing the key words). I checked the official document on the parameter Availability, but still not sure what is the proper value to feed to it in order to retrieve both current available and unavailable items.

For example, below code could not find Neutrogena Moisture Rich Sunless Tanning, which was no longer on available. However, item's information is still available here.

import amazonproduct
config = {
    'access_key': 'access_key',
    'secret_key': 'secret_key',
    'associate_tag': 'associate_tag',
    'locale': 'us'
}
api = amazonproduct.API(cfg=config)
items=api.item_search('All', Keywords=self.product_name, ResponseGroup='Medium', Availability="PROPER VALUE")