Don't forget to always visit your friends, and public market. You will often find items in other cities as well.
Most importantly, the NPC friend/city ALWAYS has 6 items for sale every 24 hours. 1 of those items will be from the category of non-makeable/non-purchaseable items (items to upgrade inventory, expand region and now beach property expansion items.
Make sure you regularly check the market. Though you may not be getting lucky, others may be and are more than willing to sell. Be prepared to be quick to the draw, and willing to spend big money on them. If you don't see an item, keep the market open and refresh it after 30 seconds (timer on the bottom)
Additionally, the game has a limit/requirement as to how many bubbles are active. If you upgrade your buildings to max and don't place new residential zones, so basically nothing to upgrade, you will get a ton of blue bubbles to pop nonstop. Whether they produce a rare item is still random however.