Blue flowers

Corn flowers?

Not sure if they are in flower at that particular time but I really love those miniature blue iris. A nice pot of those would  look the part.

I have a tiny little shrub that has the most gorgeous blue flowers I'll look & see what it's called. Lobelia comes in blue & is easy to get hold of,different shades too & not expensive.

Larkspur look like more dainty delphinium, and agapanthus come in various shades too. Both last well in water, and have strong enough stems to stick into florists' foam if that is what you would like.

Growing a pot of a short campanula might be quite nice as you could dress the plot with ribbons, if your wedding coincides with their flowering season

Most importantly, you will need something that won't wilt over a day or so. Definitely Agapanthus as I had them in my wedding bouquet and they were gorgeous. I think cornflowers, Scabious, Anchusa, Campanula (Canterbury Bells), Heliotrpoe, Blue sweet peas, Catanache (Cupid's Dart), Iris, perennial Flax, catmint, and Veronica. You could also use stems from Eucalyptus as greenery as it is blue-green in colour and would be a lovely contrast, especially if you bought some white Gypsophila to go with it all.

Blue hydrangeas. You would only need one flower head with a bit of perhaps ivy for each vase. If the stem ends are bashed or put into boiling  water for a few seconds they last well. If you had to buy a pot plant from a garden centre you would probably get as many heads as you need from the one plant.

Oh, just reread your post, and you don't like hydrangeas, just ignore me 

Blue hydrangeas. You would only need one flower head with a bit of perhaps ivy for each vase. If the stem ends are bashed or put into boiling  water for a few seconds they last well. If you had to buy a pot plant from a garden centre you would probably get as many heads as you need from the one plant.

Oh, just reread your post, and you don't like hydrangeas, just ignore me 

I've just been to a few wedding recently where they were plonked everywhere and looked awful so it's put me off