Sun conures, and indeed any parrot regardless of size, should not be given lightly to anyone, much less as a surprise birthday gift. And even less so to a minor or child. Please do enough research on keeping parrots and Sun Conures in particular before taking the plunge. Parrots are messy, pooping everywhere, LOUD (Sun conures in particular), not cheap to keep and maintain, demanding in nature and in practice, destructive and live for a long, long time. I dare say your daughter might eventually retire and her Sun Conure will still be with her. A child is not going to be able to provide what a heathy relationship with a parrot requires, including 6 hours minimum per day of out of cage time and lots of 1 on 1 time every day. They get very attached to their "person" (and it may not turn out to be your daughter!), so vacations, afterschool activities, boy friends, etc can upset the relationship, with the parrot suffering from it.
I URGE you to read the link below before going further.
I would definitely caution you before getting a conure as a gift. As @wrench13 pointed out, conures are VERY demanding birds and require a ton of enrichment time. Im not sure how old your daughter is, but if she is in school, that means the bird runs the possibility of being alone for most of the day, which could be very detrimental to the bird's health. Conures are very smart and social and do not fair well with being left alone. They are also a lifetime commitment, so you have to consider that, at some point, your daughter might be in a situation where she is unable to keep the bird, like in a college dorm or an apartment that does not allow pets. They are also expensive. I have spent close to a couple grand on vet visits with my conure Maddox when he was sick in a matter of four months. The truth is, a conure might not be the best bird to get as a beginner, especially a sun conure which are notoriously loud.
Anyway, to answer your question, after you have done ample research, the best place to find conures is at a breeder in your area, which you could find by a quick Google search.