Yes, it would be advertising. You stated the following:
"Searching and searching I only found one company that sell it on eBay"
First of all, you're making it seem as if "you" were looking for a specific item and you discovered that only one site sells it via eBay. Granted, we have no idea what it is you were allegedly searching for. Then you turn right around and say, "I'm not affiliated with the company whatsoever, would not be getting paid..."
How can you tell us you were searching for something and was only able to find it at an eBay site as if a whole lot of people were looking for that exact same unknown item? Then to want to tell everybody about that one site where you allegedly were able to find what you were searching for as if no other place sells it, is suspect, in my opinion. There are numerous places to find iPhone parts, and some of those places have been mentioned via the iMore Blog. So you see, you would be advertising. Having said that, please read the Community Rules & Guidelines to get the email address of the person mentioned therein for permission to advertise.