I have made my own by securing a piece of wire (fuse wire OK) of suitable thickness for the antenna in a pin vice securing the pin vice in something and then winding thin fuse wire tightly around it. Cut of the 2 ends as close as possible and there you are - takes all of about 2 minutes and looks good. To get the conical shape on some antennas you can use conical pen nibs to wrap the fuse wire around. I use fuse wire because its so malleable.
Failing that try Grand Prix Models (www.grandprixmodels.com) they have an excellent searchable data base and stock, or can backorder, a lot of aftermarket stuff. I have seen antenna listed in their review magazine Four Small Wheels.
Kia ora,
Mark
"Time flies like the wind, fruit flies like bananas"