Capt’n the easiest way is to make them from a piece of rubber cut from a thong (flipflop). When I made one for the Ragazza I just bought a $2.00 pair of black thongs from BigW or similar, cut a piece to rough length & shape with a knife then finished it off with a Dremel grinder. I still have 1 & 1/2 thongs left for my next project.
My IOM has a 3D printed bow bumper (using flexible filament) and you can also mould them with silicone rubber, mask up the bow of the boat up to where the bumper will fit, use silicone sealer over the bow to get rough shape & mould with wet soapy fingers to get the shape you want before the silicone starts to cure. Silicone sealer is also good to use if you make a mould first, then fill it, let it cure then remove from mould & glue into place.