Well you can make your own. You need 17.5 inches of bronze welding rod or stainless steel rod. You need to be able to solder or clamp the inner of the coax to the rod Which must be insulated to securely mount the rod. The braid of the coax cable nust be connected by as shaort a connection as possible to the aluminium mast.

Another option is to bare 17.5 inches of the inner and fit this inside an old fibreglass fishing rod piece which is clamped vertically. Again the braid must be a short connection to the AL mast itself. If you have a wooden mast or a mobo then PM me. There is no magic involved olewill