To go about recreating these, I picked up some 3/4" metal pipe crimp rings from the local DIY store. It was about $5 for a pack of 10, and I like the heft they have.
The insides of the containers were then coated with glue, and flowers from Wee Scapes were trimmed to appropriate sizes and added. Finally, they will be sealed with matte spray varnish.
They are a bit undersized compared to the real things, but my model square is going to be compressed in size, so I think they'll work out great.