Actually you are right, as of right now the only place to get door sills is RPM Tesla and to be honest I was actually impressed with it when I got it. I have not put it on the car yet on my model Y but its the same one as my model 3 and it goes exactly over the existing door sill. I even wrapped the door sill with PPF just to get it stuck more on my model 3.
I can take some pics of it if you want when I install it.