Hi legends4u,
Thanks for posting your question here. In order to get the desired category to show up when you do this category search, I believe all you will have to do is select "eBay Motors - Parts & Accessories" from the drop down menu labeled "eBay site" in the upper right hand corner of the listing creation page.
Doing so will cause the lister page specific to eBay Motors - Parts & Accessories to load and you should then be able to access the categories available on that site. When you have the eBay Site set to United States, the category search will not be able to access categories for eBay Motors.
I hope this helps. If you need any further assistance with this, please feel free to contact our customer support team by mousing over the "Help" tab within your account and selecting the "File Support Case" option.
-Mike
