It is available at all major super markets. You can also find them at Souq Waqif. While selecting one please do keep in mind that the prayer rug does not carry the picture of the Ka'aba or a mosque. This is because many people unknowingly step on the Ka'aba while the rug has been laid out. It is in view of this and as I understand, only plain prayer rugs are now available in S Arabia.
Your gesture is indeed a noble one, and may the blessings of Allah be on you.