My only option to get the natural gas orifices was to buy the tubing with it. This was easy; I simply switched out the lp orifices with the natural gas using a socket. However, I still found one burner not lighting. I came to find out by looking underneath the top that the tubing was broken. So I lucked out on needing the tube holder for that burner.
But I will mention, it would still be nice if I could have found the natural gas orifices sold separately. No one sells these separately from the research I did.