Here are some of the rarer metric units not carried in
standard reference works:

1 trillion microphones = 1 megaphone 
1 million bicycles = 2 megacycles 
500 millinaries = 1 seminary 
10 cards = 1 dekacards 
1/2 lavatory = 1 demijohn 
1 millionth of a fish = 1 microfiche 
453.6 graham crackers = 1 pound cake 
1 trillion cottas = 1 terracotta
1 million billion piccolos = 1 gigolo 
10 rations = 1 decoration 
100 rations = 1 C-ration 
10 millipedes = 1 centipede 
100 joys  = 1 killjoy
3 1/3 tridents = 1 decadent 
10 monologs = 5 dialogs 
5 dialogs = 1 decalog 
2 monograms = 1 diagram 
8 nickels = 2 paradigms
2 wharves = 1 paradox