First off is Leighton's white eyelet ruffle dress we first see her in:
You can get this similar white, eyelet dress from Laundry by Shelli Segal - here.
If you are looking for something similar, you can either find a basic black dress with v-neck and cap sleeves, and embellish it your self, or this T. Tandon dress is similar!
At the end of the movie - I loved the dress that Chiles Stanton wore when she walked into a bar (and that's all I'm going to say so I don't give anything away) . I can't find a photo or a clip of her in this dress - so you'll just have to go see the movie, but it's a blue summer dress with small floral print. Similar option via Shopbop:
Kelly's (played by Gweneth Paltrow) last concert has 3 wardrobe changes and they were all fabulous dresses. She started in a pretty red dress, with sequin embellishments and cowboy boots. I think I read somewhere (but now can't find it, of course) that this dress was specifically created for this movie/character/scene.
Similar Dress options:
Similar in neckline, dress by Nanette Lepore;
Little embellishment around the neck and similar sleeves by INC @ Macy's;
Then she wore a great black mini dress with gold stud embellishments (kinda reminded me of a skirt I got from Kohl's awhile ago).
The finale outfit was a long gold sequin dress with feather details at the bottom. Sounds like a whole lot going on, but she made it work:
You can get a de-feathered, similar gold sequin dress with a slit here.
{Movie photos from Official Country Strong site}