It highly depends on your country, some banks offer that as a service (most do in France where I live) in EU a lot of online banks do too (Revolut, Lydia, N26, etc) I don't know in the US, I think privacy.com does but I have no recommendation.
I have a capital one credit card that allows unlimited virt cards that basically can only be used at one online merchant. I use this card exclusively for subscriptions, then pay it off every month.