Well, the only 15mm miniatures I know of that will work to represent the AoA Arab list (at least certain unit types) are from Peter Pig. As I am a big fan of Old Glory, I decided to make a few of my own. I envision the dervishes as wielding large axe like weapons and swinging them in a long arc to take out multiple foes (hence the sweep attack that they get).
These are based off of some 15mm Old Glory Ansar spearmen (from the colonial range I believe).
You start with some plasticard (some thin plastic). Other somewhat flexible but rigid materials that you can cut might work as well, like matte board.
Now cut the plasticard into 4mm strips(this doens't have to be precise, wider will make for a bigger axe head).
Using a regular hand-held hole punch (my wife is a huge scrapbooker so has lots of these types of devices), punch out about 1/3 of the strip on both sides. Unforetunately I didn't take a picture of this stage, so I just made up what it should look like in paintshop.
Next you snip off the individual axe-heads that you have made with the holepunch and glue them onto the spear shaft.
That's it! You now have a dervish carrying a long axe with a huge axe-head.