I stalk the newspaper whenever I am playing. I mean I send deliveries and all that but I'm not aggressively trying to send out deliveries. I'm in no hurry to get to level 60. I only send a ton of deliveries during the events to get items to upgrade things.
Always check the newspaper. And if you score something good....always go visit their farm to see if they have anything else that's hard to come by. One other tip on getting expansion/upgrade items is to visit newer players farms when helping out to get your social rating higher.....almost all new players start selling off hard to find items since they have no barn space or cash and at the lower levels the game is practically programmed to get them a lot of these items to get them a little head start to get them past level 10 or so. I'm just guessing at that part.....but nearly every delivery they do on those first early levels gives expansion parts.