Bekhorot 21 elsewhere in Shas

Temurah 19b:15: As it is taught in a baraita that Rabbi Shimon ben Yehuda says in the name of Rabbi Shimon: An animal whose time has not yet arrived enters the pen to be tithed together with the other animals.
Bekhorot 56a:10: Rabbi Elazar said to Rabbi Shimon ben Elyakim: This baraita is not a tannaitic source that can be relied upon, as it is not accurate.
Niddah 27b:10-11: And Rabbi Yoḥanan follows his line of reasoning in this regard, as Rabbi Yoḥanan says: Rabbi Shimon and Rabbi Eliezer ben Ya’akov both said the same thing, i.e., they both issued rulings based on the same principle.
Niddah 40a:16: The Gemara answers: It is more reasonable for Rabbi Shimon to derive the halakha of a consecrated animal from a firstborn animal, rather than from the halakha of childbirth, as it is written with regard to a consecrated animal: “Its mother”
Shevuot 34a:5-6: The Gemara rejects this: It stands to reason that he should have derived the halakha with regard to an oath of testimony from an oath on a deposit and not from an oath on an utterance due to the verbal analogy between the terms “shall sin”
Shevuot 34b:16-17: The Gemara rejects this: It stands to reason that he should have derived it from the case of misuse of consecrated property, as that is a derivation of misuse written with regard to an oath on a deposit: “If any one shall sin and commits an
Chullin 83a:9: GEMARA: The mishna teaches that on the four occasions mentioned it is the seller’s responsibility to inform the purchaser that the mother or offspring of the animal he is purchasing was sold that day.
Jerusalem Talmud Rosh Hashanah 1:1:16: 151This also is from Sheqalim3:1, Notes 21–30, with an enlarged quote from Mishnah Bekhorot.

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