I couldn't find a plastic flower small enough to use for this necklace, so I improvised and made my own using several other types of plastic flowers. In the seasonal section of your Dollar Store there are usually lots of varieties of flowers to chose from.
I topped a piece of stiff wire with a small white bud off a plastic flower bunch, then I sliced a bright yellow plastic pedal into strips and glued them to the underside on the white bud in a circular array. I used another plastic vine-like clipping and attached it to the stem to give the flower some depth. I also managed to find blades of plastic grass which will be set used when the flower is set in the thimble.
Use your creative license, maybe even go a little crazy.