OP said - hard shell.
I know that you said there is "no other garden access." Does that include walls or fences? All of us dealers have had to do things to get these tubs into tight places, sometimes the client doesn't see an option which we might:
Could you lift it over a wall or fence with a small army of helpers? If you do purchase a roto-molded tub you will not be lifting much weight.
If there is a wood fence, could you take down a section? It doesn't have to be a major job: the right person could take down a section of wooden fence and have it back up in minutes. If they have experience in this type of work, the should also put it back together with screws instead of nails to facilitate removal or service in the future.
Some clients see a door through a car park or garage, but over look the larger doors through the house. Any joy on that?
Don't give up! We have gotten tubs into the most amazing spaces over the years!
HTH