As we all know shares can be supplied by borrowing them from existing shareholders, and as we've seen there can even be delivery failures when those going short are either unable or unwilling to locate and deliver the shares being sold short (naked shorting).  

Short interest for trades settled up to Aug 15th stood at 258,980 which was an increase of 17,747 from the previous period (up to July 31st).  Back in March short interest was up over 400K so it would seem to me there is room for more short selling....and with volume so low typically I imagine even just 10 or 20K shares borrowed and dumped back into the market can squelch any small rally.