I asked the pharmacist how you say foot pads in japanese while pointing to a box of them and he say they are called "jewekisheet" (jew - eki - sheet).
They had 5 or 6 brands of them and all of them had picture of the feet with the detox pads on them so its easy to see what they are (they were by the contact lenses and bandaids section but they had a thing dedicated just for the foot pads).
These things are originally from Japan so you should be able to get some for 1500-2000yen per box of 20-24.