Unisys isn't the only non-IBM mainframe supplier...
Fujitsu, Bull, Hitachi, and NEC all have mainframe businesses. I don't know enough to comment on Hitachi and NEC, but Bull and Fujitsu TS both have solid customer bases in Europe, and Fujitsu and Hitachi evidently have decided that mainframes are worth enough for them to continue fabbing their own mainframe CMOS processors.