The famous publication Karolinska krigares dagböcker has for some time been available online through Projekt Runeberg. The twelve volumes are now also online at the site Litteraturbanken, where it is also possible to search the volumes for certain names or terms, for example like this.
It should be noted that this function means searching not only the journals and reports themselves, but also the introductions and footnotes by August Quennerstedt. These sometimes contain errors, which also appear in the indexes. One significant example is in volume XII, which contains Stenbock's account of his expedition in the winter of 1702/03. He frequently mentions a certain Potocki, who Quennerstedt (with limited access to Polish works) identifies as Józef Potocki (1675-1751), the later Great Hetman of the Crown. This is however incorrect, Stenbock's counterpart was Michał Potocki (c. 1660-1749), starosta of Krasnystaw and Crown Field Writer. The story of Michał Potocki is a good example of the absurdity of the old view that Charles XII never forgot what he considered a betrayal. Potocki had made a deal with the Swedes before Stenbock started his expedition, but did not honor it. This did not stop the King from accepting him a couple of years later. Michał Potocki then fought on the Swedish side at Kalisz, where he fled. He subsequently acted rather carefully keeping his options open, but eventually joined Charles XII at Bender. So the supposedly harsh Charles ("the sword does not jest") forgave Potocki not just once, but at least twice (and possible even three times).
Charles was much more of a politician than subsequent historians have given him credit for - partially because they (just as Quennerstedt) did not fully understand what the sources told them. There were a lot of Potockis and Lubomirskis in early 18th century Poland and the sources must be carefully analyzed in order to separate them from each other.