First, please note that the belief in revelations after the Holy Prophet does not whatsoever imply revelation of new religion.
According to Shia Islam, prophets do not leave wealth as heritage but same as the Quran says their heritage is divine knowledge from God. Likewise Prophet Muhammad PBUH left his divine knowledge as a heritage for Imam Ali a.s. This is the reason Imam Ali a.s. throughout his life was never caught saying "I don't know" for he inherited the full wisdom of Prophet. It is narrated that Sahaba always asked him questions and Sunni Caliph used him as their consultant to solve their problems by the divine knowledge that the Holy Prophet left for his chosen heir, Ali. Imam Ali had wonderful judgements and was known as "the wisest of the Sahaba" by Sahaba. The book Nahj ul-Balaqa is a collection of his sayings, sermons and letters to Sahaba like Muaviyeh, Umar,... The content of the book is revered for its beautiful style, impressive eloquence and for containing wisdom about a whole range of topics from theology, revelation to ethics and history and is described as "the brother of Quran".
For fulfilling the guidance of the Ummah after the passing of the Prophet, Imams are also able to receive revelation. However such revelation does not contain any thing about a new religion or law. But rather it helps the Imams to rightly interpret and explain the religion of Prophet Muhhamad PBUH and therefore preserving Islam from corruption due to wrong interpretations.
There are many Quranic clues for why this is not strange, for the Quran already teaches us that people other than prophets can also receive revelation. The Arabic root for revelation is "wa ha ya" which in many verses is used about people who are not prophet.
Mother of Moses PBUH was not prophet but the Quran says he received revelation:
وَأَوْحَيْنَا إِلَى أُمِّ مُوسَى أَنْ أَرْضِعِيهِ فَإِذَا خِفْتِ
عَلَيْهِ فَأَلْقِيهِ فِي الْيَمِّ وَلَا تَخَافِي وَلَا تَحْزَنِي
إِنَّا رَادُّوهُ إِلَيْكِ وَجَاعِلُوهُ مِنَ الْمُرْسَلِينَ
And We revealed the mother of Musa, saying: suckle him, then when thou
fearest for him, cast him into the river and fear not, nor grieve.
Verily We are going to restore him unto thee, and shall make him one
of the sent ones. http://tanzil.net/#28:7
If mother of Moses PBUh can receive revelation so the saint daughter of prophet can as well.
The companions of Jesus PBUH were not prophet but the Quran says they received revelation:
وَإِذْ أَوْحَيْتُ إِلَى الْحَوَارِيِّينَ أَنْ آمِنُوا بِي
وَبِرَسُولِي قَالُوا آمَنَّا وَاشْهَدْ بِأَنَّنَا مُسْلِمُونَ
And recall what time I revealed to the disciples: believe in Me and My
Apostle, they said: we have believed and bear thou witness that verily
we are Muslims. http://tanzil.net/#5:111
If Companions of Jesus PBUH can receive revelation Indeed companions of prophet can as well. So according to these verses there are other forms of Divine Revelation other than those that are specific to Prophets. Therefore there should be no wonder at the Shia belief that a non-prophet or some of the pious companions of prophet or Imams receive revelation. If Wahhabi scholars claim non-prophets cannot receive revelation, it is them that should provide evidence for their claim.
Although there are books in the name of Al-Jafr but Al-Jafr originally is the name of a science and has its own usages in regards with Imams' roles. However it does not contain anything about any religion after Islam.
Al-Jafr is said to be the science of the unseen and performing miracles and esoteric knowledge. The other two books you mentioned contain hadiths and likewise not any revelation akin to the special status of the Holy Quran.
According to Shia Islam these books do exist now and are currently kept by Imam Mahdi S.A. Past Imams during their office have taught parts of them to their students, and these teachings can be found in Shia hadith books. But the original books are with Mahdi S.A.
I hope I could help you understand. But if you had been read above verses carefully you could see revelation is not limited to prophets. But it only needs being a real pious Muslim.