I think I understand the situation here. You cannot feed oyster shells to the chickens as a calcium source since your religion views the oyster as an unclean (yes, not the actual religious word but close enough, my humble apologies for the generalization). If they eat the shell, they then take into their body the uncleanliness and anything they produce, such as the eggs or a fried chicken dinner, would be unclean. The chicken, in a sense, would be the middle man.
There are two ways one can go about this. The first is to use an alternate source of calcium. The easiest one is to recycle the egg shells. I let mine sit for a hour or so on the counter (no washing at all) and then smash them with the palm of my hand on a cutting board. Some pieces will be really little, others about the size of a dime. In other words, I make a eggshell jigsaw puzzle. These, complete with any dried egg that may be on them, get tossed into the feed bucket on my next trip to the coop. Double check the ingredients on your feed as well. It may already have a calcium supplement in it. Also check with your feed supply store. I can purchase crushed limestone and granite combo so they get calcium and grit all at the same time. The limestone is made from calcium carbonate, the same stuff the oyster shells are made of.
Dairy products like yogurt, cheese, etc. and green leafy vegetables also contain calcium. The same with bones. I would get with the feed store on that as well. Some places will carry beef bone meal as a dietary supplement for livestock. They also carry pork and unknown assorted combo bone meal but if oyster shell is not allowed, definitely confirm the source content before you pick this option. This may also solve the oyster shell dilemma while giving you a way to provide extra calcium.
Also, double check with your rabbi. It is not the meat of the animal but a hard outer surface that protects the soft body of the creature. Since the chickens would not be eating the oyster but the oyster SHELL, using just the shell may not cause a dietary problem. If you were tossing the whole oyster out there it would be one thing but just tossing the shell out there may be okay. I do know that some of the original dyes used for garments during the time of the Old Testament were made from crushed sea creature shell (believe a purple, a blue, and a red) and the shell, especially as cleaned and processed as oyster shell is, may actually be okay once the processing is explained.
Good luck with it.