1,150. May One Violate Yom Tov to Acquire a Shofar?

Hilchos Shofar, Succah v’Lulav 1:4

It is prohibited to violate yom tov in order to acquire a shofar for Rosh Hashana use; this is true even of rabbinic enactments. For example, if a shofar is in a tree or on the other side of a river, one is not permitted to climb the tree or swim across the water to get it, even if it is the only shofar available. It goes without saying that one may not cut a shofar from an animal or perform other actual forms of prohibited labor. The reason for this is that blowing shofar is a positive mitzvah but observing yom tov is both a positive mitzvah and a negative mitzvah. Observing a positive mitzvah does not supersede observing a positive and a negative mitzvah combined. It is permitted to wash a shofar using water, wine or vinegar in order to improve its sound but one may not use urine because that’s disrespectful to the mitzvah.

Hilchos Shofar, Succah v’Lulav 1:5

The minimum size of a shofar is large enough that if one holds the shofar in his hands, it sticks out on either side. If a shofar is cracked along its length, it is invalid. If it cracks along its width, then if a size sufficient for the minimum size of a shofar is unaffected, it is valid; in such a case, the shofar is considered to be cut off at the location of the crack. If a shofar has a hole that has been filled with some other material, it is invalid. If it was filled with shofar material, it is valid provided that the majority of the shofar is complete and filling the hole did not change the sound of the shofar. If one perforated the inside of a horn, it is valid because the same kind of material is not considered an interposition. If one assembles shofar pieces until he has built a shofar, it is invalid.