Like you, I don't know if this exists. Why are you interested?
I think the symbiotic term as been superseded by microbiomes - try running your searches with changed descriptors?
You might try asking the authors of general microbiome studies if this work exists, because there as been lots of progress on human and plant microbiomes and particularly the importance of VOC signalling between the partners, please see some good review papers available on research gate.
These papers were all from research gate members, so a direct approach may help.
There is also lots going on with microbial consortia and bio-films authors of work in these areas may also be worth contacting to answer your question.
Those researching ruminant microbiology may also have incites into review in this area, as protozoa/bacterial interactions are very important in the functioning of these environments.
Doesn't answer your question, sorry, but may point you in a productive direction.
You are nearly right - if you need endosymbionts of protists, there are only a few:
Nowack E., Melkonian M., 2010. Endosymbiotic associations within protists. Phil. Trans. R.Soc. B (2010) 365: 699–712 doi:10.1098/rstb.2009.0188
Schweikert M., Gortz H.-D., Fujishima M., 2013 Symbiotic associations between Ciliates and prokaryotes. In: Rosenberg et al. (eds.). The Prokaryotes. DOI 10.1007/978-3-642-301194-0_18 Springer-Verlag, Berlin, Heidelberg
Fokin, Serra 2014. The Hidden Biodiversity of Ciliate-Endosymbionts Systems.
JSM Microbiology 2(2): 1015
If you need a wider view, try to search the term"holobiont" - there was a book published by Th. Bosch several years ago, and several articles pro- and contra-.
Identification of Pelomyxa palustris endosymbionts. Gabriel Gutiérreza, Ludmila V. Chistyakovab, Eduardo Villaloboc, Alexei Y. Kostygov, and Alexander O. Frolov
As well look (Elena note it but I'm attaching)
Michael Schweikert . Masahiro Fujishima . Hans-Dieter Gortz in
The Prokaryotes
The last will give you main papers. Note as well papers of Prof. T. Fenchel...