Hello! This may be old information to you, and I mean no insult if the source is an obvious one, so know that first.

This question is very specific, and I don’t have a primary source. However I do have a secondary source that may be of interest to you that discusses various primary sources. I will copy the text I found relevant from the book and include as much information about the primary sources as I can, in an effort to help.

This book is 'Crossroads of Continents: Cultures of Siberia and Alaska' and it is credited to William W. Fitzhugh and Aron Crowell, published in 1988 by the Smithsonian Institution. The essay this excerpt is taken from is entitled 'Guardians and Spirit-Masters of Siberia' and the writer is credited as 'S. la. Serov'. The excerpt (I'll include the entire paragraph) follows:

"The performance (kamlanie) was the most important activity of the shaman. It varied between ethnic groups, within a single group, and even within one settlement according to the strength and reputation of the shaman. Both in Chukotka and Kamchatka, fly agaric, the mushroom amanita muscaria, was consumed, by men only, before the kamlanie. Krasheninnikov noted that the Itelmen "affirm whatever madness they may display is, invisibly, ordered by the fly agaric" (1755:109-10). The Cossack Efrem Purgin, who spent 30 years among the Koryak in the 18th century, noted that to strengthen the power of the intoxicating mushroom the participants, after eating the mushroom, "pour their urine into a bowl or cup and drink it again" (Kos'ven 1962:280). According to the Chukchi, fly agaric took people by the hand and led them along a crooked path into the land of the dead (Bogoraz 1939:5). During the kamlanie, hallucinations were often provoked by self-hypnosis through singing and drum beating (cf. fig. 153)."

The figure, shown previously in the book, is of rock art. There is an additional source that may be of interest to you in the footnotes. I'll copy the relevant part of that footnote exactly below:

"153. Pegtymel' Rock Art Chukokta: Late Neolithic-Early Iron Age, ca. A.D. 0

Rock art from the Pegtymel' River near the Arctic coast of Chukokta provides valuable information not available from other archaeological sites (Dikov 1972). The most unusual images are "mushroom people," thought to be spirits of fly agaric, the hallucinogenic mushroom used widely by peoples of Siberia in historic times." The rest of the footnote is about animal husbandry.

The sources are listed as follows:

Bogoraz, Vladimir Germanovich 1939 Chukchi (The Chukchi). Part 2. Leningrad.

Dikov, N. N. 1972 Les Petroglyphes de Pegtymel’ et leur Appartenance Ethnique. Inter-Nord 12:245-261

Krasheninnikov, Stepan P. 1755 Opisanie Zemli Kamchatki, St. Petersburg 1972 Exploration of Kamchatka. Portland: Oregon Historical Society (Translated with introduction and notes by E.A.P Crownheart-Vaughan from Opisanie Zemli Kamchatka. 1755.)

Kosven, M. O. 1962 Iz istorii etnografii koriakov v XVIII v. (History of the ethnography of the Koryak in the 18th century). Sibirskii Etnograicheskii Sbornik 4. Trudy Instituta Etnografii n.s. 74. Moscow: ANSSSR, pp. 276-291

That took a while, so I hope it helps.