Filling in the Niches-looking for seed

I live in zone 5/6, 25" rainfall,  midwest. I have a shrub forest in the front focused on beautiful edible perennials. There's a lot of color and variety.  I have about 50 niches to fill next year.  I prefer to use seed. I am keeping it all at 6ft or less. I prune, if necessary.  So far have a lot of culinary herbs, a few medicinal, some berries, fruit, and nuts; and a few edible flowers.  I want to add rhubarb, gooseberries, alpine strawberries, (I already have the seed for the strawberries), ....what else? If you have seed or ideas let me know.  Thanks!