I had the same issue with mine a couple of years ago.
PET calls it a "steering shaft bearing". Apparently the version for '77 and beyond is different than the '76 and earlier. The part number it lists, 911 347 041 00, seems to have been superseded by a couple of different part numbers:
901 347 223 03 - "rubber mounting"
(and)
911 347 045 00 - "needle bearing"
Good luck to you. I simply walked into a local Porsche used parts place here in SoCal called Einmalig, showed them the old part, told them where it came from, and the owner of the place walked out with a good one two minutes later. Cheap too. I'm sure they have more of them. Here's their website:
http://einmalig.com/