How to convince my parents to get me contact lenses?

I'm a kind of daughter who is always shy for her parents to get her something she needs/wants. I'm a young cosplayer since I was 6 and I need wigs and contact lenses to be a better one. I secretly tried my aunt's lenses and it was fine. I think I tested it more than 10 times (not on the same day). I'm so shy to convince them to buy me a pair. Can someone tell me some tips on how without asking them? I want them to say something like "Sweetie. You want some of those? Sure, I'll get you one *smiles*" I'm 12, by the way and my friend who is also a cosplayer and 13 wears lenses. I'm from the Philippines. Thanks in advance!