Riser bolt kit: 420693 (comes with different length bolts to work with the spacers)
Extension clamp: 423509
Pad brackets: 437029 (replaced 420488)
So if you are just trying to replace the clamp bolts, just order kit # 420693
Sounds like you need 420492 then. I did mention that part # above on your post as well. It must have been missed.
Mitchell Mathews | Community Manager | Trek Bikes | @mitchmathewz