Are these available for installed cabinets? Or do the cabinets have to be new construction?

I think a good carpenter or cabinetmaker could retrofit toe kick drawers, but he/she would have to be willing to work on their belly and have slender enough arms/upper arms to work in a 4"-high opening. Opening up an existing toe kick is not without risks because you cannot always predict what is under the cabinet, yet generally it will be an open space between two sidewalls or the left and right side of a separate toe kick box. I find that I need about 1/2" below the drawer box/face in most cases because floors are often not level. If you install a TKD in a normal 4"-high toe kick, by the time you subtract the drawer bottom, you typically will not have much more than 3" of usable height left.

In sum, to get the kind of storage you see here, you need custom cabinets built. The TK drawers above were made to fit into a 7"-high toe kick. (Counters are 38"-high.) The guides are 24"-long full-extension. The counters above are 30"-deep--my standard counter depth--with 27"-deep drawers in the cabinets below.