Soft toothbrushes

I always see regular or hard toothbrushes, but never soft, at every single store I shop for when getting toothbrushes. Is this the same throughout all of Japan? Do they even make or at least sell soft toothbrushes?

Yes, they make and sell soft brushes as well. They'll typically be labeled in Japanese. Where are you shopping?

It often struggle to find soft type toothbrushes due to less demand.
I use the Lion Between soft type toothbrush but is only available at Seiyu supermarket I can only find. The other shops sell only medium and hard type toothbrushes.
My dentist told me not to use hard type toothbrushes, they are not good for teeth and gum.

I have tried at a number of different supermarkets, 100 yen stores, the home center, and the drug store...

Surely they had at least one or two options with soft bristles. Did you ask any of the store clerks for help? Well if you're not having any luck at your local stores, then many try ordering them online. Amazon japan has a good selection.