What Kindof Milk Supplement To Give Newborn Kitten?

i read about it on internet but i can’t find any info here in the stores. my cat is 11 weeks old and she drinks water only. please help me

My cat has been eating canned kitten food for several months now, since his brother died at 5-months-old. He is now 7 years old, nearly 8. The canned food came without a problem until today he ate something that made him throw up everything he’d eaten so far. I have no idea what could be causing this problem! He’s not sick, doesn’t seem hungry or anything… Just throwing up golden yellow things inside of his mouth after every meal….