Brophy's book on Marlins has several pages written up on the 1892. You might try to see if your library can get it on an interlibrary loan program as it is a rather expensive book but worth it if you're into Marlins. I use mine pretty regularly. The main gripe I have about the book is there is no serial number listing for dating a friearm.
As for parts, Numrich Arms lists many parts, including both firing pins, for the 1892. Go to
http://www.e-gunparts.com/productsch...odel=082Zz1892 for a schematic and a parts listing. Swapping out firing pins is relatively easy. Just takedown as normally and remove the bolt and replace the firing pin.