I don't quite understand what you mean...
When the ImageList of v2.0+ has been set up for 16x16 and 32x32 images (use the "New resolution" button in the ImageList editor) then images missing of a specified resolution will be scaled from the other size provided. Since upcaling usually produces poorer quality than downscaling it is recommend to provide as many images as possible in the larger size. The same image at several sizes can be added to the ImageList simultaneously by using the "Add more resolutions" button and multi-selecting the corresponding icons in the file dialog (in any order). (Therefore it is a good idea to store the same image motive at all sizes in the same directory, and not to collect each size in the same directory -- what I did initially...)
I usually get icons from the icons8.com site (
https://icons8.com/icons). Using a "Custom..." button they can be scaled to any size < 100 pixels before downloading. The download window also allows to install an offline tool which makes it very conventient to get the images by drag and drop. The icons are free, a link to their site must be provided, though (
https://icons8.com/license/) -- no idea if this is LGPL compatible.