the only pre-1899 Nagant revolvers I have ever seen were all Belgian manufacture and in Fair to Good condition (at best. . . I'm being kind). There is no "source" for them. When they were last available (about 10-12 years ago) in bulk they were twice the price of the Russian Nagants (and those were in as-new condition). "Rode hard and put away wet" best describes the Belgian made Nagants I have encountered.
Tula did not begin manufacture of the Nagant revolver until 1899, so you won't find any Russian-made 1898 or earlier Nagant revolvers.