You may use the stand-alone offline
BIP-39 generator , but vanity addresses you want, more likely, will lurk in derivation paths. Thus, it will take time for finding them manually via search.
Manually? I do not think he will find it at all. He will need a tool that can generates the BIP39 seed phrase, the keys and the address like the incoleman that you mentioned, but also search for customized addresses among billions of generated addresses. That will have to be automatic.
However the script of this generator is open source and you can modify it a bit by including parser to find the vanity-alike addresses in automated way.
I agree with this.
Also that it is worth know to use the offline version on an airgapped device.