I haven't a clue, but I've heard of people buying from it before in the US with no problem. It may depend on the seller and if those tapes are secondhand the sellers might not want to ship outside Japan.
Quite an interesting thing though, because I'm pretty sure Japan wouldn't get what it's about without the TV series, and it's probably been rewritten for them like the German release was (there's no way anyone living in Japan would get the Price Is Right joke at the beginning of the movie credits for This Island Earth)