Visit sheet music stores in your area and ask if they have orchestra parts and scores for your piece. If the store does not carry what you are looking for, a knowledgeable staff member may be able to direct you to a local supplier.
Visit a local flute shop, if your area has one. Flute shops often specialize in hard-to-get flute scores, so a member may be able to find or order the parts of "Fantaisie Brillante" for you.
Peruse Internet sheet music websites. Many have a dizzyingly large collection of scores and parts, and this may help you find the orchestral scores and parts for "Fantaisie Brilliante."
Check websites that specialize in flute playing and sheet music. These web sites may be where you can buy the orchestral scores and parts for "Fantaisie Brillante." Such web sites are often operated by experienced and knowledgeable flutists who take pride in carrying uncommon sheet music finds.