Sort of. Registrars will either apply to registries or be appointed by registries to offer particular TLDs.
Be aware .us.com isn't a TLD- somebody (CentralNIC) has registered the domain us.com and is offering subdomains (they also offer subdomains of .de.com and .eu.com amongst others). There is always the danger they can stop offering the service (like web.com have recently done) and you'll lose your name.
I'd advise you to get a .us rather than a .us.com (if you're eligible, of course)