Hi Barb,
Campanula punctata definitely can have seeds saved from it. Once the flowers die off. A pod will develop. Once the pod starts to turn light brown, little holes will appears. Pick them then. Small brown disk type seeds will be inside.
Salvias vary in how much seed they make. They all make seed in the same way. The flower falls off and the calyx is left. It becomes like a little seeds cup. At the base of it, seeds will develop. Some varieties make no seeds or one seed per flower; some make 2 or 3 seeds per flower. Seed is normally ripe when the calyx starts to brown/gray. You will seed small dark round to oval(depends on type) ball type seeds.
Remy