The search of domain name options runs as it follows. Every time after you request for some domain, service query more than 500 different sources. Shortage of speed can be caused by exclusion of domains that have been reserved by the original provider.
Usually, there is no offer of premium domains because it doesn't have a big sense. Nowadays, you can use a lot of cheap options for domain names obtaining.
But it is possible if you come across premium domains, but in order to register them, you should contact directly the TLD registrar. It can happen if you search for widely-used words or names. They are often reserved by registrars to sell as a premium. If you have other issues with purchasing a domain, please, email us at http://support.short.cm/