The hv30 is 43mm and I think think the 35a was either 58mm or 72mm depending on which you had. Once you know your sizes B&H would be a good place to start looking.
The Letus35a may not look so hot on an HD camcorder. There are other adapters that are relatively cheap that are designed for use with the HV20/HV30 like this: http://www.hv20.com/showthread.php?t=2825.