Sure Rumtea 
Principially you could use every tube in matching size, that means 16" x 1,5 or ETRTO 40-305,
I’d recommend you google for “Schwalbe” tubes, perhaps you’re able to find them locally.
The correct type of your desired tube is Schwalbe AV2 or Schwalbe Art. No. 10407310
You may check with the Schwalbe tube finder and here are original tubes:
Strida Canada/16" tube