I haven't yet purchased it but I just found this site:
http://www.laptopjacks.com/view_part/IBM-Laptop-DC-Power-Jack-IB201525.html?gclid=CMnz38ShzqwCFYUbQgodbjytpg
That looks like the power jack needed.
Ah, here is another one, which includes the little cable-- the above does not.
http://www.machinaelectronics.com/store/buypart/IBM_Thinkpad_T42/DC-P001
I haven't yet purchased it but I just found this site:
http://www.laptopjacks.com/view_part/IBM-Laptop-DC-Power-Jack-IB201525.html?gclid=CMnz38ShzqwCFYUbQgodbjytpg
That looks like the power jack needed.