Homemade chalk ?

Are there any substitutes for climbing chalk or something similar that I can get at Walmart or something? 

Browsing Amazon, it appears that classic blocks of gym chalk can be had for ~$15/lb

Browsing some pottery supply shops, it looks like raw MGCO3 starts at about $8/lb, but could contain heavy metal contaminants and may or may not have a favorable particle size distribution when used for climbing. No idea. Become the guinea pig! 

B Francisco wrote:

Are there any substitutes for climbing chalk or something similar that I can get at Walmart or something? 

I am going to assume that this is a bot post.

Walmart has a product just for your needs