100MT was not limit, this desiwn was just proof that there is no limit on nuclear power anymore. And since deuterium is quite cheap, as well as depleted uranium used for amplification, the cost is very low.

delivery is not problem either, submarine or torpedo, or just simple ship an do tha esily. of course that will be suicidal mission. gigaton range weapon probaly do not require delivery at all. in any case all humanity will die, no matter where is location of explosion.
these kind of wepons are not for attack but for defense from inteligent life forms. unfortunately and fortunately terorists dont count being inteligent, so they cant make such things, and nobody is going to make them for sale.
Original usage was simple, if we die we will destroy all earth. but as I see that is fine for suicide bombers.

Anyway with today technology and knowledge is quite trivial to make nuclear weapons, plutonium enrichment can be made even at home, however th bigest problem ir to stay alive while you do that, and pay the bills for electricity. also raw materials are not possible to get easily. but if you own nuclear reactor that is no problem.