This quick video shows the best route to most of the RC car stores in Hong Kong. The vast majority of stores are in the Mong Kok area near Kwong Wah Street.
As stated in the video it's best to get off at Yau Ma Tei MTR station and take the route in the video. This route is quicker than leaving via Mong Kok station and avoids as much of the crazy Mong Kok crowd as possible!