Do you not have a parts catalog for your airplane? If not,
here is an online generic version. Your mechanic might even have one. Once you have a catalog, simply find the correct page that illustrates what you need (maybe page 130 or 132 in the linked manual, depending on aircraft serial number). There should be a number for that item ( possibly item 44 or 45 in the linked manual, depending on which page is for your serial number). Now go to the parts listing and get the part number for that item using the number from the illustration. Once you have that part number, you can either do an online search or call your favorite parts dealers.
Or you can have your mechanic do the research, order the part and install it. <-- Best idea!
It really is that simple.