The best way would be contact Roman Catholic Diocese of Łomża.
Generally, in Łomża files from the years 1870-1890 are in parishes.
From what I read (here genealodzy.pl/PNphpBB2-printview-t-6047-start-120.phtml) this time frame you've mentioned could be at parish office Dworna Street 25:
Someone said that in order to get more help, an interested person should mention about a donation during a phone call - and a written requests may be ineffective. Then at the place, the knowledge of Russian is necessary since big part of archive is in that language.
Check also this link from Poland State Archives: