This has always been a tricky one for me to spell (although I've no problem eating the stuff, and am even trying to grow my own broccoli in the garden this year), so I was rather surprised, after poking around a bit in OhioLINK, to find a mere six examples of our cruciferous typo of the day. Furthermore, fully half of these were references to the 2004 book by Vivian Cook: Accomodating Brocolli in the Cemetary, or, Why Can't Anybody Spell? (The first one helpfully includes a 246 field with all three intentional bloopers written out correctly.) One instance of "brocolli" also showed up on a record for the Tall Dwarfs LP Weeville, which contains a song called "Mr. Brocolli." Without further research, it's hard to know whether that spelling variation was intentional, unintentional but accurately transcribed, or misspelled by the cataloger.
("Brokolice" or broccoli plant, from Wikimedia Commons.)