It is very difficult to know how much gold is really sold short because many trading houses are holding spread positions due to arbitrage trading. Also most of the positions seems to be OTC derivatives.
Here is a summery of the open Interest for the COMEX (NY) , CBOT and TOCOM (Japan), Options are not included.
COMEX (CFTC) : 361,704 x 100 oz = 36,170,400 oz
CBOT : (12,404 x 100 oz = 1,240,400 oz + 4,853 x 33.2 oz = 161119.6 oz) = 1,401,519.6 oz
TOCOM : 342,873 x 33 oz = 11,314,809 oz
COMEX + CBOT + TOCOM = 48,886,728 oz
BIS OTC DERIVATIVE REPORT REVIEW
DERIVATIVE OTC REPORT OCC