Plastic covers for mudflap screws ?

The snow caused my flap to move around alot. It seems I lost 2 of the plastic cover caps over the mud flap screws. Any help on where I can get them ?

 

After accidentally ripping the front 2 mud flaps off, I purchased the mud flaps and the plastic cap inserts from Toyota. I think they are like $5 from the parts department at Toyota. I'm sure you could probably get something from Autozone or something like that for cheaper that would hold just as well.