as for out of stocks,it is because the price of bitcoin is over 9000 (>11.500 actually) and the company struggles to satisfy the demand
they also used to sell one or more of their batches for BCH (Bitcoin Cash) only
some of the sudden stocks could be the returns or cancellations or even repaired warranty miners
and you will not be able to order one or two miners from them,most likely,they prefer to deal with the bulk byers nowadays