The best option for me as a Canadian who has travelled to some (not all) of the places you listed, is to do the exchange in your home country and bring plenty of cash with you. If you're going to Vietnam, you bring VND with you that you acquired from your home bank. Going to Morocco, bring MAD with you.
Good to be Canadian, I suppose.
Never see any such currencies in my local exchanges.
Maybe, there are some banks where you could ORDER such currency as VND or MMK, but I'm afraid, rate will be disastrous as it will be very special order.
