Besides buckwheat (white is fine, too), I would also like:

anemone sylvestris
aster, especially alpine, and others
gaillardia
erigeron (Santa Barbara Daisy/fleabane)
sea thrift (armeria)
mimulus
astrantia
lobelia
bee balm
poached egg plant (limnanthes)
ageratum
joe pye weed
ice plant (lampranthus)
goldenrod, tall-growing
helenium
heliopsis
stock
phlox
dianthus (any including carnations and sweet william)
yarrow (any named mixes)
vincas

Please check my tradelist for any seeds you're interested in.