Janie Kushon , Before replacing the box, try cleaning all the battery contacts with a pen eraser(a little abrassive), blow out all dust and debri and insert a good set of new batteries and try. I did not find a replacement laugh box, but did find a few used replacement Elmo,s that you could remove the box from or if Elmo in good shape keep your old one for parts and use the replacement Elmo. You can also try a search for replacement laugh box and maybe have better luck. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
http://www.ebay.com/bhp/original-tickle-me-elmo
https://www.amazon.com/Original-Tyco-Tickle-Elmo-Vintage/dp/B006QZNFFU