I have found that music helps my son with ASD and ADHD cope during meltdowns and is a great motivation to encourage him. There are some apps available and have a wide array of instruments to practice. However, Actual instruments are always best.
http://www.musiciansfriend.com/.
Musicians Friend is a great place to find all things music. I can search for product that is available near my area.
http://www.musiciansfriend.com/.