Is it possible grandma took them off the clothesline for you? husband is fussy about not leaving pegs on the clothesline, especially wooden pegs because they can go manky in the rain and stain your clothes. In summer we leave a few plastic pegs only, on the line, to hold beach towels.
Also I have found that on very windy days, my clothes are ripped off the clothes line and pegs missing, landed who knows where after the wind did its damage.
I hope you can find out what happened. If you need to replace them, buy a different shape made from different materials. They will be less likely to get stolen by someone wanting to build things with them.
Or you could check the next church bazaar stall, look for those families of dolls made from pegs...
Marg