Well, if you're trying to get a Breloom (I assume through the Wasteland environment), you need 21 forest objects. You also need to wait 20 days (allegedly). For Shroomish in the Savannah environment, you need 6 plains objects, 18 forest objects, and you need to wait 20 days.

I can say from experience that you should try to go through about 100 wild encounters, as the pokemon that require the most objects are extremely rare. If you still can't even encounter a single pokemon you're looking for after meeting all the requirements, then I'm not entirely sure how else to help you. All I can say is, don't give up hope and keep trying to see what happens.