Copy and pasted from Bitmain's official Facebook page:

David Schmetterer Wish I could buy just one... The pair thing is a high barrier!
Like · Reply · 1 · 6 August at 20:19

Bitmain: You have to order at least 2 units, but you can pay for one. Sales guy will confirm your order manually.
Like · 3 · 6 August at 20:48 · Edited