As you know Spektrum does not sell a replacement attenna for the DX3C.
Well it turns out you can buy a DX2 or DX3 replacement attena for about $12.95 on ebay etc. with a little findling it is a perfect fit in a DX3C. you just have to take the swivel apart and swap the mast into the swivel on you DX3C. just did it yesterday. everything else is a perfect match.