Flowers are very popular raw material, but are an effort to pick in enough quantity. It is common to need as much as half a bucket of flowers for a gallon of wine, so it is not surprising that dried flowers. seem a more practical choice.
The other annoying thing about flowers is that they have a nasty habit of being poisonous. Always check first. The list is long, and includes notables such as daffodil, rhododendron and bluebell.
Below is a list of possibilities. For bizarre and archaic reasons, petal quantities are measured in pints.