You will have to obtain a suspension rod and spring (SLarose, Timesavers, Merritts, etc. have them) and fit it in the slotted pin. They are held in place by either a dimple in the top of the spring (see pics above of the broken spring and you will see the marks the split pin has made on the spring. Just above that there is a small dimple made in the spring). Another way is to punch a tiny hole in the top of the spring and fit a tiny wire through it This wire will do the same job as the dimple. New springs will usually have one or the other so you will not have to do it.Good luck with it, let me know if you have further questions.
If you have a MS punch and scrap Ms's laying around you could make one. You may have to use a little heat to help in the bending. You can also buy spring wire on line and bend your own.