Is there a book available in stores that can be used for self-study of Tajweed rules? And is imitating the recitation of a specific person considered mockery of the words of Allah?

Among the most important books on Tajwid are: "Hidayat Al-Mustafid," "Al-Tajwid Al-Muyassar" (available as audio), "Al-Burhan fi Tajwid Al-Qur'an," "Tuhfat Al-Atfal" and its commentaries, and "Al-Muqaddimah Al-Jazariyyah" and its commentaries. One can also utilize the teacher's Mushaf (Al-Mushaf Al-Mu'allim), the Holy Qur'an Radio, and the printed Tajwid Mushaf. There is no harm in imitating the recitations of skilled reciters to learn Tajwid.