We don't have synonyms for triallist yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are trialist, tribalist and trialling.
(n) :
Alternative form of trialist. [An advocate of trialism, especially with reference to the proposed creation of a state comprising Austria, Hungary, and a Slavic region.]
(n) :
Alternative form of trialist. [An advocate of trialism, especially with reference to the proposed creation of a state comprising Austria, Hungary, and a Slavic region.]