I've only found one in a box of pennies. Had to buy the other two to fill the spaces in my album. Only missing 70-s small date from circulation now that I think about it.. Got a nice XF 09-vdb in the same box as the steel cent, and a 88-d reverse of 89.
So far I've found a 36 doubled die (die one) cherry picked from my local dealer, a 1960 d over d, small date over large date, a 1995 doubled die, and one each 2000 and 1998 wide AM. Plus last year I found and sold a 1969-s doubled die. I don't think I'll be able to top that one.