There are also
QMX-Clips that clip onto the switch: working like a landing pad for the downstroke and silences also the up-stroke.
They are of course much more expensive than the landing pads and they work only for Cherry profile keycaps because of the thickness.
There is also a cheaper type of QMX-clips for PCB-mounted switches, and Zeal PC once used to have a different type called "Zealencios".
Otherwise, if you could find the right type of foam I I don't think it would be too difficult to make landing pads yourself with a hole punch and scissors.