xfrog has some free stuff to download. You have to sign up.  I downladed some cherry tomato plants and a peach tree.  Among other downloads.
Just download the OBJ and FBX files, then use 3DXChange or CC3 (create accessory, then detach in iClone.   Free 3D Tree and 3D Plant Samples: Xfrog.com

KKVIZ on CGTrader has some outstanding free samples ( most downloads include 2 or more samples of that model).
Use the same example above to download and convert. I try to stay away from over 500,000 polygons and vertices. But I may download some.
You have to sign up with CGTrader. They give you about 10-20 items to download for free. Then after that you either have to submit a model or give 
100 reviews on some of the models. If you like it and review it, that counts as 2. I have already reviewed hundreds. But if you don't know how to make 3D models.
this is one way of getting some free 3D assets into iClone via 3DXChange or CC3. You won't be disappointed. 
Free 3D Models by KKVIZ | CGTrader