You could start by using the month's flowers - June is rose, September is Aster.
There are books on the language of flowers that might give you a hint (might find some online free)
There are plenty of roses to choose from, look through a catalog. Aster family includes sunflowers, mums (Japanese fabric?) June is the time of the summer solstice, so anything involving summer would do, September is autumn equinox, so there's plenty of fall stuff available.
HTH.