Most of us have a multiple razors. I keep two in a case that I alternate between every day. Cased pairs are two razors in a case. Sometimes two of the same razors and some times two different.
This is the first one I found by typing in cased pair straight razors in google http://www.thesuperiorshave.com/dovo_85705_pearlex.html
I don't think SRD actually sell a cased pair but they do sell the case so you could probably work out a deal with them if they have razors you like.