Storm on inside??

I have a 20 year old home with insulated aluminum double hung windows. They have screens on the outside and glass , moveable and removable storm windows on the inside.
I have never seen this type window and I would like to get a few for an addition. I cannot find a name or number anywhere.
Any adeas?

Sounds like triple track? Don't know if they make that anymore.

The triple tracks I am familiar with also had the storm window on the outside.

Why not just get double or triple pane windows in the same finish and eliminate the interior storm window ? A lot easie to find and you'll have two fewer panes of glass to clean.