I'd like to know if there where in Finland any publications of books written by Polish author Boleslaw Prus?

You can find two titles written in Polish by Boleslaw Prus: Faraon and Lalka. The books are available in Helsinki City Library. (HelMet database : http://www.helmet.fi/ ; database of Helsinki, Espoo, Vantaa and Kauniainen city libraries).
There are also some publications at Helsinki University
Library. You can find more information about these books at http://helka.csc.fi/webvoye.htm (choose "search" and then "basic search", write Prus Boleslaw and choose "author", you'll get 18 books plus some different editions of same books).