Question: My barbarian will be level 3 soon, and I'm looking forward to choosing the Path of the Totem Warrior.

Answer: 
The most thematically appropriate option would be for your Barbarian to hunt the relevant animal of your choice. 

The PHB of 50 states

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> You must make or acquire a physical totem object -an amulet or similar adornment—that incorporates fur or feathers, claws, teeth, or bones of the totem animal. 
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Your choice of totem animal is Bear, Eagle or Wolf. 

In order to facilitate this I would speak to your DM and set out what type of totem you wish to get, and ask if they could facilitate a hunt scenario for this particular animal into your campaign.
You need to acquire the item:

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> You must make or acquire a physical totem object -an amulet or similar adornment—that incorporates fur or feathers, claws, teeth, or bones of the totem animal. 
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From [Merriam-Webster](https://www.merriam-webster.com/dictionary/acquire):

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> **acquire:** to come into possession or control of often by unspecified means - *acquire* property - The team *acquired* three new players this year.
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And by *unspecified means* it can include **buying one**. In any sufficient large city there should be a shop of trinkets, oddities[,](https://www.grammarly.com/blog/what-is-the-oxford-comma-and-why-do-people-care-so-much-about-it/) or magic components that can sell either the amulet or the required animal parts.