I need to buy the plastic gear selector w/key and mower switch where to find

Hi,
The STX38 has two versions. The shift quadrant for the yellow deck version is M74797, the cover is M77392. For the black deck version the quadrant stays the same, but the cover is M119935. The covers are called instrument panels in the descriptions.
Those are Deere part numbers. A Deere dealer would do, or perhaps eBay.
Peace,
Clarke