The most likely places for a pulley is related to the lift system. I would recommend going underneath and doing an inspection to see if you can notice any visible area where the pulley is missing. Most of the pulleys are located right at the hydraulic lift assembly and also at the points of where the cables go up at each corner of the trailer. Hope this helps out in trying find the spot where it came from, good luck. I also found it easier to get around underneath my trailer with the use of a creeper, they can usually be found on sale at harbor freight, I bought mine there for about $20 and worth it, especially in Arizona.
Former Owner of a 1999 Classic HiLo Model 29B