I broke a bass spring on my Bb Swallow box. How could I get a replacement quickly?

Quickest is to make it yourself. Take out the broken spring, and match it to a safety pin the same diameter and size. Clip the ends to the same length, and bend a 90 degree 'foot on each leg, matching the ones on the broken spring. The feet go in those tiny little holes opposite each other, and you're back in business. If you order one, at least you won't have a dead bass till it arrives.

Steve

That's exactly what I would do if I were you. If fact, that exactly what I'd do if I were me !
As I think about it, I AM me, and that's exactly how I make the bass springs.
Jude

When using a safty pin to replace a bass spring, if you need more tension spring the safty open wider before installing and this will increase the tension.

This Should have read, open the safty pin wider to get more tension.

Clever!