You will never be able to get the correct tuning of the maqam scales on the piano. That is because the notes of the piano are tuned to Equal Temperament
http://en.wikipedia.org/wiki/Equal_temperament which is a tuning scheme that was developed for Western Music to enable modulation to all 12 chromatic keys.
The Arabic tuning system, on the other hand, is based on a Pythagorean scale
http://en.wikipedia.org/wiki/Pythagorean_tuning - in other words, the fourths and fifths are perfect, or "Just," based on the harmonic frequency ratio of 3:2 (in the case of fifths) or 4:3 (in the case of fourths). This is unlike the tuning of the piano. The typical oud tuning is C F A D G C, and the correct tuning of those intervals is as I just described, with fourths (C to F, A to D, D to G, G to C) resonating perfectly. Fourths on the Piano don't resonate perfectly, instead they are based on an irrational frequency ratio, which is in fact 5 times the 12th root of 2.
The other notes of the Arabic scale, on the other hand, are variable culturally. Although we call them "half-flat" and "half-sharp," they are not precisely halfway between anything. Only in an Equal-Tempered scale (see above) are half-steps precisely equal to 1/2 of a whole step. In the Arabic scales, there are half steps and whole steps of different sizes, each of which must be learned by ear. The so-called "3/4" steps are in between the size of a "1/2" step and a "whole" step, but not exactly halfway. In Syrian music, the sikah note tends to be higher than the sikah note in Egyptian music. In certain maqamat, the sikah note is higher than in others. By my count, there are around 12 different notes in between the smallest half-step and the largest whole-step, so there's no way to fit all of those different notes on the piano.
The following podcast has audio demonstrating and discussing this issue in more detail:
http://maqamlessons.com/analysis/media/PPerform_019_2007-02-02.mp3 String instrument that don't have frets, like the violin, viola, cello, bass, oud, etc. can achieve any possible note, just like the voice, and so they are very suitable to play Arabic music, since they can get all of the varieties of intonation used in that music.
Some Arabic Keyboards have the capability of playing quarter tones, but most of them are out-of-tune with the Arabic maqam scales as most traditional musicians play them, because those keyboards are actually based on the Equal-Tempered scale with quarter-tones added (and in that case the octave is broken down into 24 equal 1/4 steps). Although this scale was first theorized in the 19th century, at the 1932 conference of Arabic Music in Cairo, Egypt, it was demonstrated that this scale is out of tune with the scales actually used by Arab Musicians.
So my suggestion for anyone wishing to learn the arabic scales, who doesn't play a fretless string instrument like the violin or oud, or who isn't playing one of the other Arabic instruments designed to play the microtones used in the music, is to
sing the scales. Match pitch with any source with your
voice.
But avoid using a piano at all costs - it will train you to have bad intonation.