.rs is a new domain extension and available for pre-registration with licenced registrars. In case of need for help with translation/registration, I can help DP community for free. Tip on choosing registrars: some registrars accept your pre-registration money but will not refund it to you in case they do not get to register the domain when the time comes in January, and your money is stuck to register some other domain or domain extensions with that firm that likely is to offer a way more expensive .coms etc than GoDaddy, NetFirms, go with the registrars that do refund you money in case they do not get to register you .rs domain you applied for. Most good domains will be gone seconds after the January registration begins, those who are targeting good domain names go with pre-registration or hope that targeted domains will not be taken in the pre-registration period.
Serbia (.RS) three new tld's were anounced on September 11, the other two were: North Korea (aka Korea, Democratic People’s Republic) (.KP) Montenegro (.ME)
Previous domain extension was .co.yu. Those domain names are not automatically transferred to .rs, current owners will have forehand in registering the same .rs. The number of .co.yu domains was limited due to the fact that only business owners could have registered them, some of those businesses do not exist to this day, some had transferred to gTLD, some don't use their .co.yu domains, and other scenarios, majority of .co.yu names are not English words so for example football.rs is available for registration.