You don’t make it unless you have a lot of time on your hands, you buy it. I have a tub of it from the last kayak I built.
The principle use I’m aware of nowadays it to mix with epoxy to thicken it for applications in boatbuilding like stitch and glue construction.
Most marine supply places or places that sell epoxy will have it.
It easier to make silicone molds and cast in foam urethane. More durable and quicker, but the old fashioned wood flour and hot hide glue works. Either way, you will have to do some staining or painting. Urethane can simulate wood pretty well if you prime with a flat grey spray auto primer and then brush stain it with dye stain and overcoat with an acrylic stain like General Finishes. Practice on any primed surface.
Edit. Use a couple drops of detergent to get the flour to absorb water.
Add Silica to make it flow better. ( available from the same sources)