Pesachim 9:8

If you have a korban pesach that got mixed up with other karbanos, you let it pasture until it gets a blemish and then sell it. Since you don’t know which animal was for which karban, you must take the most expensive and use that amount for every single korban involved, adding money from your pocket as necessary.

If you have a korban pesach that got mixed up with a bechor [first born], R’ Shimon says if your group is made up of only cohanim, they can eat it.

Pesachim 9:9

If a group lost it’s korban pesach and sent someone to go find it and bring it as the korban and he found the korban and brought it, but meanwhile the rest of the group bought another animal and brought it as the korban, if the original korban was brought first, then that is the korban for the group. If the groups new korban was brought first, for them it is the good korban and the original one is just for the one who brought it himself.

If when they sent this person out to find the korban he said, ‘if I come late make a korban for me’, and they both brought korbanos, if the groups korban was first, they all eat from that korban. If his korban came first it is good for him and theirs is good for them. If we don’t know which one came first, the groups korban is good for them and he cannot eat it and his korban must be burned as it cannot be eaten since maybe he is part of the group. However, he does not have to bring a pesach sheni, as somewhere he had a good korban.