You can get username on comments sections of the resources and for the full name you have to do some extra digging using that username.Most of the time people use same alias name as username on many different forums and social sites.The chances are 50/50.If you can't find it using this method.
Then make a gmail account similar to seller and email the people saying that you are increasing the product support for the item from 6 months to 2 years and to they need to provide their full name to receive this offer.