This might sound dumb, but if the phone number belongs to someone else now, could you just call/text them and explain the situation and (eventually) ask them to read you the code or something? Admittedly it'd sound suspicious as heck, but if you're willing to provide sufficient proof of your identity and somehow offer a reward in a safe manner, the person might understand and be willing to help? You'd have to be pretty smooth about it, but it seems worth preparing for and giving it a try.
Alternative idea: If you're really desperate, you could even try to dig up the phone number owner's address and show up at their door or something and explain it that way. (Note I'm not recommending these per se; I'm just pointing out what's possible. Obviously be very careful to consider everything before doing such a thing.)
I received a call one time with a SOB story about someone locked out of their yahoo email account with my phone number, which I've had for over a decade. In the back I could hear people talking, person had a thick accent from a country known to scam people. I knew it was a scam so I started probing more and they finally hung up.
It is a super bad idea for anyone to give out 2FA codes, they could easily found your email associated with a specific number from a security leak and attempt to steal it.
You contact them and ask them to reset your login details. You offer $100 and you give the username to them asking them to complete the password reset procedure.
You'd trust the current owner of the phone number to be honest (because you are contacting them), not the other way around.
I'm not sure what context Google provides in those text messages, but if it is just a one-time code; how would I know, you aren't trying to log into one of my accounts?
This is literally why I said it would sound suspicious. Most people wouldn't be able to tell. Which is why I said you'd need to provide some kind of sufficient proof of your identity (or some adequate alternative) to address their fears.
Fantastic suggestion! Definitely a great option if they're willing to take the risk.
If not, another one I was thinking was asking them to meet at their local police department and looping in an officer into the story or something. Different things work for different folks so they'd have to get creative to find the right solution.
I would be very wary of associating multiple Google accounts together. You don't need a single mistake from your personal account to cause a closure of your business account - and Google is known to do that. I recently had "nicer" auto_corrected to "ni66er" (Android keyboard swiping) even though I've never used that racial slur in my life. I could see how that might set off a chain reaction leading to account closure.
I'm not sure if this is intended to be a joke or something else, but I'm fairly sure knocking on someone's door or calling them without solicitation for something like this isn't a crime.
SMS text messages could be intercepted (ab)using SS7, which is the protocol interconnecting the various phone carriers. You "just" need to get access to the SS7 network... hard but by no means impossible.
Alternative idea: If you're really desperate, you could even try to dig up the phone number owner's address and show up at their door or something and explain it that way. (Note I'm not recommending these per se; I'm just pointing out what's possible. Obviously be very careful to consider everything before doing such a thing.)