Depends on the use of the tins. I use a cheap unit that requires the heat to come from the pot that I heat on an induction stove to bring to the boil and then get heat through the meat etc.
I would suggest that you measure the inside diameter and go to a local cooking store or even Kmart and measure the cake tins etc available.
You do need one at least that can hold the water to produce the internal heat unless you wish to run on some sort of power.
Nothing ventured nothing gained. Any utensil that holds the excess outside the heating pot should work, whether it sits inside the existing or on top of a new set.
Remember the set of containers in the old pressure cookers that sat inside the pot to hold the vegetables?
Will be interested what others say.
Regards
Brian

Soup tins, with the tops cut off and sharp edges gotten rid of, works well. Cover well with foil, tying with string or rubber band - three soup tins fit in my Ecopot!!