Where did Cain and Able get spouses?

Answer 1

The Bible did not openly say that Adam and Eve had other children, but it is assumed that they had more sons and daughters besides Cain and Abel. Therefore, they probably married their sisters, and had children. (the Bible mostly recorded the firstborn males in a family)

Additional Answer:

In the antediluvian world, brothers and sisters married in order to populate the Earth. This continued for a short period of time after the Flood when marriage laws were effected as there were enough people in the genome pool:

Genesis 5:1-4New King James Version (NKJV) The Family of Adam5 This is the book of the genealogy of Adam. In the day that God created man, He made him in the likeness of God. 2 He created them male and female, and blessed them and called them Mankind in the day they were created. 3 And Adam lived one hundred and thirty years, and begot a son in his own likeness, after his image, and named him Seth. 4 After he begot Seth, the days of Adam were eight hundred years; and he had sons and daughters.

Answer 2

Cain killed abel, and Cain married his sister

Answer 3

Gen 1:27 So God created mankind in His own image,

in the image of God He created them; male and female He created them.

28 God blessed them and said to them, “Be fruitful and increase in number; fill the earth and subdue it. Rule over the fish in the sea and the birds in the sky and over every living creature that moves on the ground.” This was BEFORE Adam & Eve!