What's that stuff you put on flowers to make them stiff?
You didn't say what kind of flowers so I'll address both silk and dried.
You folks are going to think I have stock in Plaid ... the Mod Podge people ... but, really, I don't. The stuff to use on silk flowers is called Petal Porcelain. It's made by Plaid and you can find it in your local hobby store. It is a water based stiffening agent that you can use on silk flowers. It goes on milky but dries clear. Then you can paint the flowers with acrylic paint if you want and spray it with varnish or coat it with a glaze. The Petal Porcelain also acts like a glue so if you don't stick the flowers right to your project you'll need to put them on wax paper to dry.
You can try a liquid polymer, such as Crystal Sheen, for dried flowers. This is a two part compound that you mix up and then pour over items. I have no idea how this would look though. It says that one coat of this equals 50 coats of Urethane varnish. So it would be shiny!!! You'd probably have to order this online.
Hope this helps,