Yes, you have missed the boat here: Go does not have any built-in
package manager, and `go get` is not one.
Please consult [1] for the list of 3rd-party tooling which are real
package managers.
You might also find digging through the archives of the sibling Google
Group, "go-pm", to be of interest.
1.
https://github.com/golang/go/wiki/PackageManagementTools