Can I buy Apple Watch series 6 model A2376 in us

Apple doesn't sell that model in the USA due to differences in cellular band support. If you happen to find someone else selling it in the USA, ensure that it's not activation-locked before giving them your money.

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Based on what you posted, do you live outside of the US? If so, do you have a US-based credit card to make the purchase with? If you do, then potentially you can buy the Apple Watch at a physical Apple Store. If you plan on buying it via Apple's online store they will not ship it to another country. In that case you can have it shipped to someone in the US, and then, have them ship it to you.