Do you mean you want to search within a specific TLD and get a list of domain names? If you're searching within a TLD would you want it to return:
or www.someco.tk, mail.someco.tk, vpn.someco.tk, etc.
How do you plan to deal with Dynamic DNS services? It's highly likely that people and companies within your country depend on services like dyndns, no-ip, etc. none of which would fall within *.tk.
Because there's no point in searching for a given extension (TLD) as the list of TLDs is pretty much static unless ICANN et al make some major changes.
Seems that I am not the only one still missing the point of what you want to do exactly. Well too bad then I am keeping the scripts for myself.