Hi I find it very important to buy the courtesy flag in the country I am going to.
It's always one of the first things I do... Clear in and go find a news agent with flags for sale. They are more than impressed when I go in and explain why I want their flag and get them to tell me why it looks as it does.
I always buy the cheap school kids flag on a stick... Never the marine grade flag. The Bahamas was a classic example the flag on a stick was $2 and right next to it was the marine grade courtesy flag for $22!!!!
I have never been hassled by customs for not having the flag up when I arrive, but on one occasion mentioned it to the officials, saying I could have bought it overseas and made someone else richer, or wait till I get to your country and buy your flag form one of your own people.
To attach them to the flag halyard I just use a couple of slim cable ties.