I included some links and the companies from which you can purchase blood agar
However I wanted to ask whether your child’s science fair allows blood agar because usually it is not considered viable for a student to use because of the potential of contamination from people. Students commonly use are Nutrient agar and LB(Luria Bertani)Agar.
I included the information regarding both agar’s from the science buddy website:
Nutrient Agar-Will grow the largest number of different types of microbes - fungi and bacteria. Yet, not all bacteria can grow on these. Some find it too rich, and others find it deficient. The nutrient in this is beef broth, and some extracts from yeast.
LB Agar-A subtype of nutrient agar, this is the general medium for microbiology studies and may be used for routine cultivation of not particularly fastidious microorganisms. Also, does not preferentially grow one kind of bacteria over another. The preparation for this agar is included in this link:http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_Agar.shtml
Here is a link that provides the procedures needed to create your own agar medium in case you need it.http://www.umsl.edu/~microbes/pdf/homemademedia.pdf
Good Luck and if you need more clarifications or help please post.