Suggest you post this in the "Wanted" forum. I got a Tunisian courtesy flag from www.waypoints.com - in the USA. Good quality, sewn flag, but at $29 it wasn't cheap. I was ordering charts from them at the time, so the postage wasn't an issue. Welcome aboard.
If you are really looking for cheapest, easiest way is to get collins flag book or look here http://www.atlasgeo.net/flags/Eindex.htm
Get some white cloth and some water colour paints, or acrylics.
We painted our own and only had problems with one of the caribbean islands that chooses to have a parrot on its flag! just don't go to Dominica and you'll be OK.
Malta and Tunisia look quite simple red/white designs, with a bit of grey on the Tunisia flag.
I got a good quality sewn Hong Kong courtesy flag (my wife is a Hong Kong citizen!) from Mr Flag. Can't recall the price exactly, but it was about £15.
I got a good quality sewn Hong Kong courtesy flag (my wife is a Hong Kong citizen!) from Mr Flag. Can't recall the price exactly, but it was about £15.
I may have been unlucky, but I didn't find any for Tunisia or Malta on google (worldwide search) last year. Looked just now, and a total of 26 flags available; only for near EC countries or for across the pond.
If you cannot get one easily for Malta, you could always buy one when you arrive. Only some five minutes walk from where you clear customs. It would cost you around €10, depending on size. Don't worry, you won't be shot for not displaying it!
Incidentally, the correct courtesy flag for Malta is the national flag, not the civil ensign.