Is this part 214?
I think there should be 2 of these. One at the mainmast and one at the foremast. Heller instructions are rather poor so I may be reading the online copy wrong.
It does look tough to copy by making a mold but if there are 2 on the sprue and if you are only missing one of these perhaps you could make another from plastic using the existing one as a guide. If you are missing both, write a real letter to Heller, as they do respond. If you got the kit from an authorized Dealer they should be contacted to do the " leg work" for you.
There's plenty to do on this kit while you are waiting. I suspect this part could be added later, just before you start the rigging... in maybe a year or two.
Nino