Got some of those black peal balls with a spider web on them for my black spider,looks good just cant see them as well.
Rest of them i get of Mark and had no problems, $2.50 each i think.Not sure but it worth putting the old one in the tumbler or just get some new ones.Never tried it but i thought once there stuff that it throw them out 
I've put some worn ones in and they came out like new. Once they become pitted, in the bin they go.
I check my balls once a year - if pitted - throw them out - If they look good - Then chuck them in the tumbler for 4 hours !
