Is your religion one that requires a community effort?
Many of us our solitaries in our paths.
There are modern shamans who have traveled in Central and South America in an attempt to bring something back to the contemporary world, but I suppose that you are already familiar with them. So you do, in fact, find that you are alone. First, I would travel to Northeastern Brazil if you have not already done so. Do what you can to find the sacred sites of the religion. That kind of religion was undoubtedly "born" from the land. If you have no idea where the sacred sites are, study the land and follow your inner sense in order to locate them. It would help if you could talk to some of the indigenous people if they still live there. They won't tell you anything until you gain their confidence, but an old man or an old woman might know more than the anthropologists think they do. You are not an anthropologist, you are their descendant, and they might eventually talk to you. Don't expect to find much in the way of documentation, because the teachings are much more likely to be oral than written. Another approach is the direct engagement with the spirit world. Now you are the shaman or the priest. This is not a path for the "amateur". You must be both humble and courageous. Again, it would help immeasurably if you had a direct contact with the land. Find a sacred place, or a place that you believe is sacred. The sacred place is the site of rituals and other worldly journeys because it is the location of some kind of energy node in the earth. If you don't know how to take an inner journey camp there and sleep overnight. Be careful to remember your dreams. Keep a notebook beside your sleeping bag and whenever you wake up note down any dreams you can remember or any impressions you might have. If you think you can remember them in the morning you are probably wrong; the "gods" will take away your memories and you won't remember anything. Consider yourself fortunate if a wise guide tests you and initiates you. This is not an amusement for a two-week vacation; this is the work of a lifetime. The word "initiation" means beginning, and your trip to Brazil is only a beginning.
I just remembered something: the kind of religion you are discussing undoubtedly used sacred plants to enable the priest to enter the other world. But become familiar with the plants and their physical and psychological effects upon the human body and brain before ingesting something. If the religion there is still alive, unknown to the anthropologists, you will receive guidance concerning the plants. You could also dream about a plant.
Well, Epehuatl, this Folk-Catholicism can be very useful to you, as such practices always incorporate the underlying pagan traditions. It would be useful to you to document such beliefs, but not in a manner that would insult these people (such as pretending to be a believer in their faith). Eris Epiphanes has given you very good advice, and I would also add that although sacred plants are parts of many traditional religions, you should exercise extreme caution, because if you approach a sacred plant with the wrong intentions, it could drag you body and soul into the spirit realm, permanently.
I myself am a solitary out of necessity. You might find that living the life your ancestors lived will lead you on this path you desire to follow. As a start, you might try a vision quest, something from the North American indigenous people's repetoire, but be safe and bring along a like-minded friend when you sleep out in the jungle.
Best wishes, and may you reconnect with your ancestors.
My question is, how do you know for certain it's truly dead and/or forsaken? Over the past 30 years, I've seen lots of groups and solitary practitioners of various, supposedly "dead" pagan traditions coming forward, so take heart. You might want to check with the folklore and anthropology department of some Brazilian colleges to see if they know of any leads. Good luck on your quest!
This person should have some ideas.
Oh, I'm in the same situation, though I'm on the other end of the world.
I just dig through the internet, use mentions from (their) contemporary sources, filter out the opinions and biases, and add a bit of the historic folk beliefs. It's the only thing I can do, I'm afraid, since info is so scarce. You're kinda lucky, your tradition 'died' in the 17th century, mine 'died' back in around the 4th or 5th.