Roger,
I'm pretty sure that your weep hole covers are the same as the ones on our coach. Check out the picture to make sure. They are made by SE-GI in Norco, California and the part is #133 weep hole cover - black. Just to make sure they are the same, the dimensions are - length 3 3/4" with the outermost locking tabs being 3 1/8" apart.
I found the easiest way to order from them was to call directly at (951) 737-8320. As of 10/09 they were $1.29 each.