I've also found that the ShopParks App has a wider selection of items that
ShopDisney.com, but both are more geared to WDW. In many cases (not all), if you see a shirt that says "Walt Disney World" on it, there is probably a DLR counterpart that says "
Disneyland Resort" on it. Likewise, for items that feature the four parks logo at WDW, there is often one that features iconic DLR locations. I've found that there tends to be a wider selection of items in the parks,
but they're more spread out so you'd have to visit more locations to find the full assortment (e.g., DL specific shirts in DL, DCA specific shirts in DCA). On the other hand, World of Disney is a good place to find a lot of choices in one place.
(One other note: depending on when you're going, you might be running out of time to pre-order a shirt from ShopDisney.com/ShopParks App, unless you pay for upgraded shipping. I've found that the App store purchases tend to take the full shipping window time, plus several business days to pack. So all in all, it typically takes about 2 weeks for my orders to arrive from TN to CA.)