I would buy a chameleon from a member of the forums at https://www.chameleonforums.com/chameleons-sale/ . Just make sure that you ask the breeder to give you more info on the chameleon, just in case. Also if they live around the area you could do a local pick up.
You should see if his legs or arms are bowled, and if it it loses balance, and you see him fall he might have MBD. Also if his eyes are bulging out to much it might be MBD.
I want to buy crickets, so I could breed them for my chameleon, but how big should the crickets be so they could start breeding? How many crickets should I get?