Many learners try to extend (maintain sound) too long before taking a breath. As your capacity increases you will be able to play a part without taking a breath, but it's not critical that you do at this stage.

If you have reached the stage where you're 'chantering' on the march, the suggestion above with respect to getting a goose adaptor for your GHP is a good one. Just cork off all the drones (actually I prefer to leave the bass drone operating), and enjoy periods of extended playing without the hyper-/hypo- ventilating issue.

On the practice chanter, whether seated or 'on the trot' it's a good technique to learn to take your breaths in or around the third measure of the lines, so that you are 'playing through' the ends of lines and ends of parts. That will pay off bigtime when you switch to the pipes.