In my web travels, I came across a web site ( http://www.familyfungraphics.com/ ) that offers a variety of clip art including flower clip art. The site looks new but they promise regular updates and a service where you can request custom clip art. The clip art is extremely high quality and high resolution so the images are easy to work with. There is a membership fee of $1.99. I have a feeling that as the site becomes better known, that fee will go up.
So if you don't want to bother to learn how to draw flowers and you'd rather cut to the chase and get pre-made clip art, check out http://www.familyfungraphics.com/
For those of you who are still interested in learning how to draw flowers the following web site has great instructional material available.
MisterArt.com: The world's largest online discount art & craft supply store!