How can I amplify the current out of a triangle wave generator?
Since you are already using an LM324 as a oscillator at 400 milliHz  (0.4 Hz). Just use one of the addition 2 opamps in package as a buffer amplifier with a class B output stage.





Select Q1 and Q2 based on load requirements.

There will be small amount of crossover distortion as the load current requirements change sign. If that's an issue bias the output for class-AB.