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As far as I'm aware, the only ferry operator for Lake Baikal is VSRP, and their complete schedule is here: https://vsrp.ru/en/passengers/timetable/
While both services used to operate, at time of writing, VSRP has no services to/from Severobaikalsk at the northern end of the lake or Tankhoy on the east coast. Olkhon is still served regularly.
As for private arrangements, perhaps a tour agency could arrange a chartered trip for you, but unless you have a large group the cost is unlikely to be "reasonable", since it would be 12+ hours one way from Irkutsk to Severobaikalsk and Baikal's notorious storms mean you wouldn't want to tackle this in a small boat. Tankhoy is much closer and might be more feasible, but it's also reachable by train.
Upvote:0
As an addition to the answer about the ferry company VSRP:
Severobaikalsk - Khakusy is served by a small boat whose timetable can be seen there: http://hakusy.com/transfer/ and also can be reserved there.