silverlight2004

hello, can someone tell me where/how i can buy some new counterweights (or hammers?) for the px5s? i'm talking about the black rubber piece that slots on top of the black 'tab' protruding. i have several keys that are not returning to their level position so they are now below the level of the rest of the keys. on all of the keys like this, the rubber piece is missing. In the photo the top one of the 2 has the rubber piece missing that i need several of. kind regards dave needham