• aource book,
• zource book,
• xource book,
• dource book,
• eource book,
• wource book,
• siurce book,
• skurce book,
• slurce book,
• spurce book,
• s0urce book,
• s9urce book,
• soyrce book,
• sohrce book,
• sojrce book,
• soirce book,
• so8rce book,
• so7rce book,
• souece book,
• soudce book

The adjective form of the word "source book" would be "sourcebook".

The plural form of the word "source book" is "source books"

The singular form of the word "source book" is "source book". The word does not change in its singular form.