For the plastic rivets the part number is 90467-10183. Get them from your Toyota dealer, they charge around 2$ a piece or buy a kit of Toyota fasteners from Ebay or Amazon.
Also, Lowes Home Improvement stores have a automotive fastener section (in hardware) with all the plastic shield clips and are less than a dollar each.
the 06 has a different type clip underneath that is a 7mm round hole
As far as the square holes I've seen them listed under 9mmx9mm, 10mm, 8mmx8mm
I would imagine they're the same part the hole may measure somewhere between 8-9 mm