Shrimps And Fish

@pandaman I don't have much direct experience with shrimp, but have you tried growing some algae on stones in a dish of water on a warm well lit window ledge? You can place the stones in amongst the plants on rotation. In the short-term maybe you could find a small amount of algae in a garden water butt or container but I'm not sure how you would feed it to them. Another suggestion would be to crush fish flake into a fine powder that wouldn't interest the gutsy Corys then place it directly into the plants near the roots and hope that it settles where the shrimp can get to it.
Best of luck and I hope this helps

I have amano shrimp in my temperate tanks, which also contain peppered cories. They are bigger than panda cories, but it just so happens that the shrimp in those tanks are female, and quite large themselves. I will say that my amanos take no messing, and make sure that they get their fair share.
It may be down to fish/shrimp personality, who gets put in the tank first, who thinks it's their patch, etc. It could be anything, unfortunately they can't tell us.
I'm a big fan of alga stones  , although possibly not as much of a fan as my bristlenose and blue-eyed ancistrus, who go nuts for them  . I don't give them to my shrimp as they don't have a problem with finding enough food.
I have panda cories in my betta tank, so I know they can feed anywhere in the tank (not just on the floor), but you could also try putting food somewhere towards the top of the tank for the shrimp. Make sure that they have some cover so they feel comfortable, but perhaps stick an alga wafer or something somewhere that would be less comfortable for the cories to feed, such as the underside of a leaf, so the cories would get used to eating the food at the bottom of the tank and leave the stuff at the top of the tank for the shrimp. I don't know if it would work, but it might be worth a try.