Hi Kwathi,
For spelling bee, as AC has said the best way is to pick a few words from the dictionary and learn. Not sure how old your child is. Also there is a website :
Merriam-Webster's Spell It!. I found this site very useful.
For Geo Bee: Go to the National Geography website. And you have all the resources for the Bee right there. In addition, reading the maps from an atlas is very helpful and also I found the CIA website on all the countries great resource for the Geo Bee.
For Math Bee: Best way is to practice math sums at home. You can get some books from your local library : search Math bee or Math olympiad and you should find prep work book for them.
Hope this helps.All the best for your kid.
Vandhana