How can a 15 yr old buy condoms?

I’m 15 years old and I want to buy condoms to try on, and also to maybe **** in, you know just to experiment.

I’m 13cm/5.11Inches flaccid and 17.5cm/6.89Inches erect

How do I do this?
What size to buy?
What brand?

Ps: I live in quite a small town...
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