Need help with an original challenger r/t, asap

Alright guys, I got the sending unit out and the sock looks very nasty, it is almost black and I'm sure it is probably the original one. I want to replace it before I put the sending unit back in, and the unit is fine, so I'm not buying a new one, but I can't find one at any of my local parts store. Have any of you bought one from your local dealer or parts store, or i
s this a year one part?

Thanks