I came to know Dolce Design from Glamour This Love links.
I just love how the designer uses the crystal balls to set up the mood. I adore anything that blings.
I googled rhinestone buttons and found some wholesalers that sell per 24pcs lot (good for smaller group of invitations).
Rhinestone Jewelry has nice assortment of buttons.
KV Jewels has some cute color butterflies and flowers.
For those who has tons of invitations to send out to, visit Alibaba as the min quantity tends to be 500-1000pcs.
image taken from Dolce Design