Perhaps you can fabricate your own keel guard. The method would be:
- Apply some release agent to the keel or even a layer of very thin plastic wrap;
- make a impression mold of the keel, including any portion of the stem that you want to protect;
- using the mold, create a plug which will serve as a mold without having to use the actual hull;
- using the plug, laminate your own keel guard using the appropriate materials and resins
- remove the keel guard from the plug, and trim it to have a uniform edge and size
- affix the keel guard to the boat using a strong adhesive
You could also attempt to apply the chosen material for the keel guard directly to the hull, but I think the method I propose of making a plug will be easier to actually laminate a keel guard that will exactly fit the hull than if you tried doing on the hull itself.
As for what material to use to make the keel guard, I suppose you could use carbon fiber, but that advice would be tempered by a tendency for carbon fiber to loose strength with abrasion. KEVLAR might also be appropriate.
There are also commercially available kits like these from Keel-Eazy
https://www.keeleazy.com/collections/keeleazy-storeand
https://www.keeleazy.com/pages/faqsI have no experience with this product, but it looks easy and does not cost a fortune. The material used is apparently able to CONFORM to the shape of the hull bottom to which it will be adhered by an adhesive.