Twar, It appears the same ebay seller is still selling them and he certainly sold you PK shrimp. So that means they are hiding in the vegetation and you need to net in the grass in the shallows when the water warms up, or they were eaten or displaced or something.

I have seen the PK shrimp with a strong light in the shallows at night. Their eyes glow a bit under a strong light.

But on the other hand most of us would love to have the Gammarus sp. too. if your pond keeps a thriving population of the scuds that isn't too bad for a trade off or is it?