If Da’esh or any other Islamic group which controls territory, resources and industry, genuinely wants to institute gold as common currency; it seems to me that the logical preliminary step would be to establish trade relations with those countries where gold is abundant, and stipulate that any imports from that group’s territory must be purchased with gold. This will boost the group’s supply of gold, enabling them to actually mint coins for domestic circulation.
The obvious trading partners, of course, would be poor African countries with a significant natural gold surplus.