Personally, I'd boil the solution and filter it boiling. Repeat a few times. You'll have almost all NaCN at that point in solution. Then cool down to ice temp and it will crash out. This works because the solubility of NaCl at 100°C is about 37g/100mL H2O, and at ice temp it's about 35 - a flat solubility curve. Do we need to remind you of the dangers of cyanide salts?