|Some adult elbowpads may fit your knees?
For my kids, I use:
-teens ones from decathlon.com: they have agressive sets (knees/elbows/wrist) at 30euros and helmets too, but seems they are not in US!!!
-some adult fitness kneed pads could fit agressive too.
The main concern was to find pads that stood in place (wearing the pant under can help too in winter).