It's easy to make a pattern if you want to.
Use silicone RTV two part system which is a pourable liquid system that cures at room temperature to cure into a flexible rubber.
Mask off an area of good pattern to the size you want but I would suggest no bigger than about 100mm x 100mm using something to make an open box for containment. I would suggest rigid plastic like a piece of old cutting board for example. Tape it up to seal it with gaffer tape or similar, the rubber is quite viscous so should not leak out too much and thickens up quickly while curing anyway. You want to make the mould about 15-25mm deep for strength and to make it conform to the pattern when in use for repairs.
Wax the surface that you intend to make a mould from to allow release of the Silicone Rubber RTV using normal hull wax
Mix the RTV as per instructions (usually they are 1:1) take care not to introduce air bubbles while mixing.
take a brush and brush the mix into the area to be copied, take care to fill all the spaces and "wet out" the area to stop voids forming during pouring. Once done carefully pour the mix into the box and let it stand until cured (probably a few hours) .
Once cured the pattern will be a flexible rubber with hopefully a perfect female representation of your anti skid deck. You can then use this in-situ after putting on some gel coat to make the shape or if you have larger damage you can make a separate gel coat surface which you can then use on your deck after grinding down the area you want to replace.
Here is a video from You Tube. This was just one I found during a quick google search and I am not associated with the company. I am retired from a larger manufacturer of silicone elastomers and used to be in a technical role.....
https://www.youtube.com/watch?v=SBjAF4axDoY