I am so happy to hear from the many would-be ballerinas of the world. Many of the concerns I get asked about have to do with pointe shoes. The local ballet store may not carry many brands, and ballet students may have trouble finding exactly the right fit.
If you asked a world class ballerina if she got exactly the right fit from shoes made just for her, you might be surprised to find that even they do some work on their pointe shoes.
Seeing that many stores have no shoe fitter, or one with the same problem as you have - limited stock - it is a good idea to step on a piece of paper and draw your foot outline. Both feet - since most people have a different shape or size from the right foot to the left. This gives you and the fitter an idea to start choosing shoes from.
Of course other factors then come into the picture. High instep or low, will determine how deep a shoe you need. Long toes, short toes, uneven toes, will determine the length, width and shape of the box part of the shoe - the part that will encase your toes.
Flexibility of the ankle joint along with the general mobility of the arch and foot bones will determine how hard a shank you need. Since shanks can be softened, it is better to try a harder one, if you are in doubt.
The fitter or helper will show you how to point your foot in the pointe shoe, with the platform on the floor, without putting weight on the shoe. You can do this sitting or standing. It's always good to try on the pair - remember that feet are not mirrors of each other.
Try whatever toe padding that the store will allow. It's idealistic, but unrealistic to plan on taking pointe class without any padding at all. Ouchpads, Lamb's Wool, toe spacers or levelers if you have a long second toe or long big toe, are not just luxuries. They will protect all your foot bones by distributing your weight among the toes in the best way possible.
Pointe shoes are not meant to fit quite like a glove. Snugly, yes, but you must be able to do a demi plie in fifth and second position without excruciating pressure on the ends of your toes. On pointe, the toes should not be loose in the box (too long or too wide) either, or your feet will not be supported.
Even though this sounds like getting exactly the right fit is a tricky risk, it is not. If you have few brands to choose from, you can find a workable fit. Breaking the shoes in properly and good foot care matters too.
More importantly, be sure you are ready to start ballet classes in pointe shoes.
Pre-pointe exercises should be done for a few months. If your teacher, parents or your health practitioner have any doubts about you being prepared for pointe work, it is better to wait. Sufficient strength is paramount.
Students who are no longer growing have the extra advantage of ordering on line and trying different brands.
Ballet stores that supply small local schools will not carry every brand available. Understanding how to accommodate having a smaller choice with patience, and knowing how to fit the shoes will get you what you need.