There is nothing on a TZ that even slightly resembles the small plastics, possible marketing ploy 'buy our 7 piece kit' with 5 useless pieces 
I would stick to rivets as I like the original look, but other than small button head screws, you could use dome head socket screws like these:
Pop down to your local fastners shop and have a chat with them.
Oh well, I really only bought the set for the 2 large plastics anyway, and the set wasn't much more expensive than buying the large plastics on their own so no biggie.
I would like to use rivets too, but I don't have the right tools or skills for riveting nor the rivets themselves. I was hoping there would be something like those dome head screws but without the socket hole i.e. a smooth head that looks similar to the original rivet head, albeit a bit bigger
Matthew
