I do not know of any site that does not allow us to create an account prior a purchase. If we are required to register a domain to create an account then they should say so or at least respond to my query. I sent them a question (a support request) and they did not respond. So that is the past.
Today I tried to register a domain, one that is not likely to be registered. It said that the .gk is available. I clicked on Select and then it became unavailable. I did that for a more obscure domain. Same thing. Then an even more obscure domain. For that one it said that all of the free domains are available but each time I clicked on Select each became unavailable. They obviously have disabled the ability to register free domains, at least for those of us without accounts.