Hi Lotte,
I once went to Bolivia for one month and participated in Ayahuasca ceremnies and other ceremonies (dancing from sundawn to sunrise, sweat lodges, pilgrimage, cleansing rituals). This is the link to their website:
www.sacharuna.com. It changed my life ... emotionally and spiritually. I participated and was there with 15 people from all around the world. It was so special. This organisation is trustworthy. The shaman is Miguel Cavlin ... if you contact them, don't be surprised that the information flow is slow; that's how it goes over there. Don Miguel doesn't give lots of information during the "training" ; you have to experience everything yourself, and you will if you go. Another possibility is Peru, Don Augustin ... he is Miguel's old teacher and he gives more explanation, that's what I have heard and he should a great shaman too. If you prefer not to go on your own, there is also a dutch organisation who organises trips to South America, with local shamans. The organisation is:
www.qoyatika.com.
Hope this helps you a bit further. Good luck Lotte !!