Here be Kaiserreich era maps (oh, how I long for any source with constituency-by-constituency results, rather than lists of winners. 
None seems to exist, in print or over the net. The Constituencies remained unchanged throughout, so this should be an easy task... The guy who made this site looked at official gov't publications from the relevant election years.)
http://www.wahlen-in-deutschland.de/akurtwalg.htm
As for such wishes and longings I know of this:
-Caramani, Daniele and Peter Flora 2000: Elections in Western Europe since 1815: Electoral Results by Constituencies. London: Macmillan.
The volume comes with a CD-ROM giving full documentation of Reichstag election results for major parties by constituency. In Excel and SPSS formats (I think).
However as electoral cartels of parties within the same or similar political camps have been quite common then and were usually agreed on in the individual constituency and ignoring this could lead to seriously misjudging the results, one might also wish to consult
-Reibel, Carl-Wilhelm 2007: Handbuch der Reichstagswahlen 1890-1918: Buendnisse, Ergebnisse, Kandidaten. Duesseldorf: Droste.
Which is a 2-volumed-exercise in documenting each and every cartel we know of, at constituency level for every election and by-election 1890-1918; in German though.
And for doing it really really really properly (since these cartels often covered both Reichstag- and State-elections), one would have a look at (e.g.)
-Kühne, Thomas 1994: Handbuch der Wahlen zum preußischen Abgeordnetenhaus: 1867 - 1918; Wahlergebnisse, Wahlbuendnisse und Wahlkandidaten. Duesseldorf: Droste.
