Available for reading online or download here: https://archive.org/details/1968-04_202210/1963 04/
A few issues are missing. August, September, October, November 1965, and April 1971 on to the end.
You can find the covers to all issues here: http://99wspeedshop.com.s3-website-us-west-2.amazonaws.com/modelcarscience.html
Internet archive has many interesting books and magazines. Car Model is also available, but only to read online if you log in.
Look around, you will be pleased with what you find on both these sites.