I think Lewis had oriental culture in general in mind- Islam is a relatively young religion in a place that has seen civilisations come and go long before Mohammed.Tashbaan is an oriental city ruled by despotes, but some things like pictures and statues of a god is not at all islamic and despotisme doesn´t fit in with sufisme.Aravis and Rabadash believe themselves to be descendants of the god Tash- that would be an obscenity for every muslim. We tend to identify Calormen with Islam because Islam is a religion connected to the Orient and calormen is the Orient in the world of Narnia.What is astonishing is that we only see the bad things Lewis describes, but their are also positive things. He admits that calormen have a great style in tellling stories,a great but somewhat sinister and cruel civilisation: that calormen can be very brave- even Rabadash is, Emeth and Aravis are also and both are described as upright and reliable.
About information about Islam- their are relatively good sides in the Net in German, where muslims try to explain their religion and culture to Europeans, but I do not know if something like that exists in English.
Hmm; little test if you really try to find information:
After the islamic calendar I was born on the 17th day of the month Safar in the year 1377.
How old am I and when is my birthday in our calendar.
?
Iustitia est ad alterum.