I wouldn't suggest even trying to find peonies and lilacs at this time of year as they're strictly a spring/summer flower, but if you're getting married in spring time and want some inspiration for centrepieces you could make yourself, then look no further...
You will need:
Two cube glass vases, one large (6") and one small (4")
One small square of floral clay (approx 4" by 4" x 3/8")
4" square flower frog
5 floral stakes
2 bunches of peonies (approx 10 stems) in two shades of pink
1 bunch of lilacs
1 bunch of miniature kale
2 bunches of thin asparagus
5 baby artichokes
2' pink and green ribbon
An awl (or bradawl)
Double sided tape
Place the floral clay in the centre of the larger vase and the smaller vase on top of the clay. Asparagus stalks should be cut to approx 5" before being placed in between the two vases. Use a pick or skewer to scoot them closer together. Add water to the outer vase so all stalks are covered by at least 1".
The flower frog (a heavy piece of lead with small spikes that sits at the bottom of the vase and holds the flowers in place) should be placed inside the smaller vase.
Cut off the stems of the artichokes. Push the floral stakes deep into artichoke centres so their weight will be fully supported. If the artichokes are very hard, make an initial hole using the awl.
Fill the smaller vase halfway with water (2"). Cut peonies, lilacs and kale to 8" to 10" and slot them randomly into the flower frog so they stay in place - longer stems should be in the middle so they stick up, shorter stems on the side so they curl under.
Artichoke stakes should be cut to 9" or 10.5" and inserted so they sit higher than the flowers. The arrangements should look very full.
Choose a ribbon that pulls together the colours used. Attach double-sided tape to the back on both sides and wrap around the square vase, assuring it is centred before affixing.
** all images and concept from Epicurious via DIY Bride.