Trackpoint Iv basically comes on any Lenove X, t, and W series dating way back.
Trackpoints typically are not found on just any Thinkpad, they usually need to be a corporate/business grade laptop, hence the X, T and W. I wouldn't go older than an X200/T400, anything older is just useless today, and would recommend a 220/420 simply because the memory is so much cheaper that they can balance out on cost, and you still end up with a faster processor with more ram.
You can often get other corporate/business class laptops with them as well such as Dell or the HP Elitebooks, however I can't find any info as to the trackpoint version, however I can't imagine them continuing to use a version several years out of production. Some Sonys also had them (again, not sure what brand or version), but with how Sonys hold their value and repair costs I hate to recommend them.
If you just want cheap with a trackpad IV, look for a T420, you can find them dirt cheap missing hard drives and/or memory, I once got one for under $50, just needed a drive and power supply, both of which I had. If you want a mini-monster system, get an X220 (look for the IPS screen), toss in an SSD or two (yes it can have two) and 16gb of ram, if you get the I7 you even get USB 3. The X230 is similar but all models have usb 3. Any of these will keep up with modern ultrabook as they used full voltage processors, and they handle Linux incredibly well. I was getting 5 hours out of my X220 on Mint on the 6cell (flush) battery and 9 on the extended, just shy of the battery life in Windows.
