Measuring Solar Cell Short-Circuit Current with INA219
You can make your own current shunt. Typically current shunts are 50 ~ 100 mV to limit power dissipation.

If you are expecting 50A or 5V across 0.1 Ohm then let's make a shunt that is 50mV @50A = 5W.

Always choose the high current shunt max rating to be starting range of ~ 50~100mV depending on heat rise and space allowed. and % of voltage

**edit to reflect question late change


using formula for 100mV shunt can be 100mV/250mA= 400 mΩ 1/2W R . Then use gain x25 for 2.6V full scale @ 260mA.. yes you should have said that up front... then meets IC limits, or 50mV shunt uses 200 mΩ 1/4W with gainx50 
**


R = 50 mV/50A = 1 mΩ   Pd=50A * 50mV = 2500 mW

Look up AWG gauges suitable for 1 mΩ.

AWG16 = 4 mΩ/ft   = 13 mΩ/m


We also would like to make it non-inductive as possible so a wire pair with opposing current is a good approach in close paired or twisted pair wires.
Thus to make 1 mΩ choose AWG16 pair about 2" (5cm) long and short the wires at one end and pass a known current using meter and measure voltage drop to calibrate your current shunt. Then strip and cut open end length until calibrated using 10A or so with a meter to check.  ( twisted Magnet wire is best for low inductance but any wire is OK for DC.



  
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  .  ===========|  {Shorted wire pair shunt resistor}
  . ===========|  {"Kelvin method" means sense inside connections}
  /
  warning: ascii art dwg.
  


Use calibrated DMM to calibrate shunt with known current.

For use after calibration, ensure twisted pair wiring with ferrite sleeve to reduce CM noise and orient sensor wires at right angles to high current wires.