I think Tiger lilies (something like that. they have pretty lily-like flowers and grow on long graceful stems) can grow pretty fast and the pollen was easy for my friend to collect. (used a cotton swab).

Sunflowers?

How fast are we talking???? Lilies are slow. You would be better off with a shortday type flower like: zinnias, batchelor buttons, marigolds etc….

crocus, paper whites, tulips, any bulb can be forced (by refridgeration) or you can go to the local florist & buy some already grown. Their pollen can be collected rather easily.

Marigolds are very fast growers.