Purchase new software via purchasing?

Purchase new software via purchasing?

We've been using SD for a few years now and we're trying to begin using the purchasing module. I'm trying ot purchase new software that is not currently managed but when I attempt to add a new product it presents me with a list of all scanned software. We don't have this software scanned because I'm trying to purchase it.
 
Is there a step I've missed? How do I purchase software we've never had before or had inventoried?

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