It is customary to use a section of a fowl's neck bone.
We are also particular NOT to eat the Zero'a during or after the Seder.
The sixth Rebbe of Lubavitch, Rabbi Yoseph Yitzchak, would remove almost all the flesh from the Zero'a.
This is to avoid any similarity to the true Passover Offering of old, which may not be brought nowadays.
Where can you get a shank bone for Passover? Having trouble finding one.
Kosher meat stores and supermarkets should have them in stock soon, you can reach out to the stores in the large city closest to you. Or purchase online on Kosher meat suppliers. Alternatively you can use a chicken bone, Trader Joe's has kosher chicken.