As far as I can see, the **30 is indeed the last where most (all?) of the drivers are available for XP, from Lenovo. E.g., your X230:
https://pcsupport.lenovo.com/us/en/products/l … ds/driver-list/
Already the **40 series has almost nothing official for XP:
https://pcsupport.lenovo.com/us/en/products/l … ds/driver-list/

That does limit your options in getting a modern Thinkpad with a built-in numpad and XP support. Maybe the W701. It's a brick, rare, expensive, and has a first generation Core i7, which is not terribly efficient. Still, being a quad core, it will outperform your X230 in some tasks.

Lenovo T430. Not only does it support XP, but you can also disable Nvidia Optimus from the BIOS, so you could use the laptop's NVidia discrete graphics with Windows XP.

Problem is, it's almost impossible to find new.

Yes, I guess T530 is the way to go.

And yes, I actually was looking for a used Thinkpad and I don't mind getting used ones, since these Thinkpads are actually built like tanks (well, at least the IBM ones) - "Tankpad"! 😁:

Both my T42 and X230 are bought second-hand. And they are still rock-solid. I upgraded the screen on the X230 from TN to IPS, bought from ebay, and upgraded the backlit keyboard.

Thanks again.