How would one go about finding the Norton equivalent current for this?
The Norton source current is just the current that the circuit would deliver to a short-circuit (0-ohm) load.

So if you have the Thevenin voltage, \$V_{th}\$ and the Thevenin equivalent resistance, \$R_{th}\$, then the Norton current is just 

$$I_n = \frac{V_{th}}{R_{th}}$$

If you don't already have the Thevenin equivalent circuit, then you could re-draw (at least mentally) your circuit with a short across the outputs, and find the current through that short. It would be equal to the current through \$R_1\$ plus the current through \$R_3\$, both taken from left to right.