Does anyone have any tips for replacing the rubber inside the garpoon points? It acts as the spring to deploy the barbs
I think they are latex and for the life of me I can't find any 5mm diameter latex solid cord to try.

Anyone happen to use something else?

Have you check in the slingshot or spearfishing sites.
Mechanical Maintenance handlers may also have something, also.
Good luck, and good shootin too ya!