5xx errors are server errors - something went wrong on the server. In particular, a 503 indicates that:

the server is currently unable to handle the request due to a temporary overload or scheduled maintenance

4xx errors are client errors - the client is making a request that the server is unable or unwilling to fulfill. In particular, a 403 indicates that

the server understood the request but refuses to authorize it. A server that wishes to make public why the request has been forbidden can describe that reason in the response payload (if any). [..] However, a request might be forbidden for reasons unrelated to the credentials.

I would argue that 503 is clearly incorrect, because this isn't a temporary issue - you don't support requests in that area, period. The argument could be made that you eventually hope to support the area, but the intent of the code is to include a header indicating when the client can try again. "In 6 months" doesn't adhere to the intent.

403 is a better choice because your service simply forbids requests from certain locales.

5xx errors are server errors - something went wrong on the server. In particular, a 503 indicates that:

the server is currently unable to handle the request due to a temporary overload or scheduled maintenance

4xx errors are client errors - the client is making a request that the server is unable or unwilling to fulfill. In particular, a 403 indicates that

the server understood the request but refuses to authorize it. A server that wishes to make public why the request has been forbidden can describe that reason in the response payload (if any). [..] However, a request might be forbidden for reasons unrelated to the credentials.

I would argue that 503 is clearly incorrect, because this isn't a temporary issue - you don't support requests in that area, period. The argument could be made that you eventually hope to support the area, but the intent of the code is to include a header indicating when the client can try again. "In 6 months" doesn't adhere to the intent.

403 is a better choice because your service simply forbids requests from certain locales.