Sorry I missed this. Lace motifs are really popular for embellishing dance dresses and, unlike ballroom juveniles, I'm assuming you don't have to look for a very close colour match to comply with dress regs. They can also give you a really good basis for your stoning design and are often used for hair adornments too.
All three of the big suppliers sell these motifs but they're often called different so the same search term won't work with all of them. Trim It are usually the best value (as is normally the case) and list them as
Guipure Lace Motifs, DSI have quite a few known as
Pairs Laces , as does Chrisanne but calls them
Guipure and Crochet Motifs. You can also check out the Guipure lace fabric when it's in their sales because you can cut out the motifs which will give you a lot for a very good price.
Of course there's always China too! Loads of them but you do have to wait for delivery. I've not used them because of the colour match issue and since my DGD has been in Juniors she's wanted something different. Lots to be found on Etsy as well but all US based and those that I've seen all had very off-putting delivery charges which I really don't understand as they seem to be able to send a dress pattern very cheaply and quickly which probably weighs more.
I've not listed trim contacts as that's all over the place. Plenty on ebay as well as many other online suppliers.