One of the red tshirt guys at Paris Opéra Apple Store said they have a few of the quad and hex base models in stock. Also said the 7 flagship Apple Stores will all have the Sharp 4K monitor on display (and I confirm it runs at 60Hz and it is a beauty !). Don't know which other six stores those are apart from Paris Opéra.
60Hz? The nMP/Sharp on display in Santa Monica was only running at 30Hz and display properties had setting options only for 24Hz and 30Hz... No 60Hz option.