Is there evidence for "Awliya" and "Pirs" and "Saints" in Islam? So, what is it? Do they receive revelation after the Prophet SAW? Or is it just made up?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Allah has mentioned the Awliya (the allies of Allah, the religious best believers whom Allah has chosen) in the Quran. He mentioned their attributes, characters and distinguished qualities. Allah Says about them (what means): {Unquestionably, [for] the allies of Allah there will be no fear concerning them, nor will they grieve.} [Quran 10:62]

He described their characters to make them known and distinguish them from the supporters of Satan. Allah Says about them (what means): {Those who believed and were fearing Allah.} [Quran 10:63]

Thus, whoever is a true believer and fears Allah is a “Wali” of Allah. And whoever is not so and claims to be a Wali of Allah is actually a Wali of Satan.

As for Murshids (those who guide the people to righteousness and goodness), they are the Muslim Scholars who act according to the Quran and Sunnah and guide the people to the right path; i.e., the path of Quran and the Sunnah. They are the leaders of Islam and bearers of this religion.

With regard to others who only claim to be Murshids and guide the people to the way which contradicts the way of the Prophet his companions and the righteous predecessors of his Ummah, then they are all deviant, misleading people and are not following the path of the believers. The leadership and guidance of such a Murshid is similar to the one of Pharaoh when he said to his followers (what means): {Pharaoh said, "I do not show you except what I see, and I do not guide you except to the way of right conduct."} [Quran 40: 29]

The word saint is an expression used by Christians to mean someone who has reached the highest degree of goodness and acceptance from their point of view. But for the Islamic Sharee’ah, anyone who does not believe in the prophecy of the Prophet Muhammad is a disbeliever, and so, he will surely enter Hellfire, be he a saint, a priest, or someone else. Allah Says about them (what means): {And whoever desires other than Islam as religion - never will it be accepted from him, and he, in the Hereafter, will be among the losers.} [Quran 3:85]

The Prophet said: “(I swear) By Him in whose hand is the life of Muhammad, he who amongst the community of Jews or Christians hears about me, but does not affirm his belief in that with which I have been sent and dies in this state (of disbelief), he shall be but one of the denizens of Hellfire.”

As for your question “Do they receive revelation;” the answer is that they do not receive any revelation from Allah, but they receive the revelation of Satan that has not been interrupted. But the revelation of Allah stopped and its door is closed forever after the death of Muhammad, the last Prophet . There is no revelation after him. The Prophet said: “I am the seal of the Prophets.” [Al-Bukhari]

In Saheeh Muslim Anas narrated: “Abu Bakr said to ‘Umar: “Let us visit Umm Ayman as Allah's Messenger used to visit her. As we came to her, she wept. They (Abu Bakr and Umar) said to her: What makes you weep? What is in store (in the next world) for Allah's Messenger ( ) is better than (this worldly life). She said: “I weep not because I am ignorant of the fact that what is in store for Allah's Messenger (in the next world) is better than (this world), but I weep because the revelation which comes down from the Heaven has ceased to come down.” This moved both of them to tears and they began to weep along with her.”

Allah knows best.