Ravi,
I don't know about commercially available pads, but you can always improvise. Some old (or new) tennis balls will work, or some rubber balls sold to kids. Not the greatest look, I admit. You are trying to decouple the physical (mechanical) vibration of deep bass transmitted from the enclosure to the floor, so a sandwich of dissimilar materials will work (sand, foam, etc.).
The problem that remains is the acoustical energy of the deep bass radiated from the woofers and the ports through the air. Acoustic energy is picked up by the sheetrock or plaster in the walls and ceiling as well as the floor, and transmitted through the sub-structure of the room and the building. There isn't much you can do about that short of turning down the volume or building a room within a room, one totally isolated from the other, which gets very expensive.
Having lived in apartment buildings of various ages and a semi-detached house, I've usually experimented to find out just how loud I can run the sound levels and subwoofer without incurring the wrath of neighbors. I avoid really loud late-night listening and turn down the sub somewhat if I think the dynamics of the music or soundtrack exceed levels I think are acceptable.
Regards,
