Here you go Mike

3/8"
https://www.alexsparts.com/valve-seal-protector-sleeves-3-8-applications-pack-of-two/

5/16"
https://www.alexsparts.com/valve-seal-protector-sleeves-5-16-8mm-applications-pack-of-two/

I tried to be all technical with the name and couldn't find anything in google. So I just typed it in as I would describe and found them.

I googled "sleeve to protect the valve seal when they slide over the grooves 3/8" and it worked lol.