tips on getting a binder without parents finding out?

In terms of how you can get money to buy it:
1. Use the credit card of someone that you're out to and trust
2. Get one of those prepaid credit cards (they're usually available at 7/11 Walmart target you the idea)
In terms of where you can ship it to:
1. Have it be shipped to a friend's house
2. Have it shipped to your regular house but use the holiday season as a cover up as to why you received a package

I'm sure there are some other ways.

 

Honestly, ordering right now is the best time (assuming you're planning on using the internet, whish seems like a good place to get one), because if you receive a mysterious package and they ask "what's in the box?" You can just say it's a secret and they'll assume it's a Christmas present or something. (make sure you actually do get them a present so you don't blow this cover later)

If you don't have a credit card you can buy gift card type credit cards at places like Walmart or similar.

If your parents are the type who would open a box with your name on it, before you get the chance I recommend shipping it to a friend who supports you, so then they can just give it to you.

All that said, I don't know your parents but if you don't think it's likely that they'll disown you or beat you or something you might just want to come out to them and get it over with. Because you'll have to eventually.