Can aqua regia/royal water be produced with sources of chloride and nitrate other than hydrochloric acid and nitric acid?
Not even zinc would react with neutral nitrate + chloride, why should gold ? 

Aqua regia must be strongly acidic for nitrates to have oxidative properties for oxidation of chlorides to chlorine and to oxidize gold to trace amounts of $\ce{Au^3+}$(what redox potential allows)

Mixing of acids leads to these reactions:

$$\ce{HNO3 + 3 HCl -&gt; NOCl + Cl2 + 2 H2O}$$
$$\ce{2 NOCl -&gt; 2 NO + Cl2}$$
$$\ce{2 NO + O2 -&gt; NO2 }$$

That also means aqua regia dissolution ability decreases with time.

The major oxidative reagent is free chlorine.  Hydrochloric acid saturated by chlorine dissolves gold as well.   Chlorides additionally help gold dissolution  by reaction $\ce{Au^3+ + 4 Cl- &lt;=&gt;&gt; AuCl4^-}$, this decreases the redox potential $\ce{Au/Au^3+}$, making gold dissolution by chlorine and even by nitric acid easier.

$$\ce{2 Au + 3 Cl2 + 2 Cl- -&gt; 2 AuCl4-}$$
$$\ce{Au + HNO3 + 4 HCl -&gt; HAuCl4 + NO + 2 H2O}$$
$$\ce{Au + 3 HNO3 + 4 HCl -&gt; HAuCl4 + 3 NO2 + 3 H2O}$$

See also https://en.wikipedia.org/wiki/Aqua_regia