Silicon valve cover gaskets?

I've heard silicon valve cover gaskets exist for my 383, but where does one buy these?
Thanks!

Why not make your own? Squeeze a 3/8" bead of black rtv around the inside of the valve cover flange and let it set til it "skins" over, set covers on heads and just start the cover screws. Let it set up overnight and then snug the screws. Prefect seal

I dont know about silicone but I have rubber ones
on my 340. Picked them up at Checker. I like them as I have adjustable rockers I look at every season so they are handy as they are reusable.

Mancini Racing has them

I got mine from summit. I put them on and for the first time ever have no leaks!