1.25x1.25u Keycaps?

[fortissim2]

Check the title, lol
I want a non-1u square keycap for one of my thumb keys for my keyboard, but I'm not sure where to find keycaps like this.
Are there stores that sell 1.25x1.25u keycaps (or something similar, preferably 1.5x1.5u or maybe 2x2u), or do I have to make it my own? Like with 3D printing or using a mold or something, I don't even know how that'll work.

[Findecanor]

The closest thing you could find are 2u × 2u  keycaps for point-of-sale keyboards, but those are made for 2×2 switches under it. They are also often relegendable. See this picture for an example.

If you want to build one yourself with a 3D-printer or sculpt, I'd suggest starting with a "Tipro MID" relegendable keycap. With the clear lid off, those are very low and flat, making it easy to put something on top.

Most people building their own ergo keyboards just use regular 1.25×1 or 1.5×1 keycaps and rotate them 90°.