Hi Mohammed, you can try shops opp old hyatt in Dubai, there you will find many shops selling and installing these DVD and nav system. Though you are from oman so i have searched one shop in google for you to get an idea of location and directions, once you are there in that market check other shops too.
They also have Touareg DVD player on their website, see if you like this option
http://www.claytondubai.com/volkswagen-touareg.html
EGHBAL SOLIMANI TRD. CO.
Tel. +9714-2727007
Fax. +9714-2711355
Opp Hyatt Regency,
Al Musalla Road,
Deira - Dubai
United Arab Emirates