You can make one yourself or better still replace the drive gear or modify yours. If you remove the PTO cover plate and bearing carrier , put both boxes in nuetral the gear will slide out with a jiggle. If It has for 3/8 holes drilled in the section between the gear and the PTO dogs just put it back in and forget it. If it doesn't check the shaft and gear splines for wear. If they are ok you can drill the gear(it's hard) useing a masonary drill bit sharpened like a normal high speed steel drill and some drilling compound. If your not keen to do this go to an engineering shop and have them drill it. This will limit further wear. If you have some wear you can change the gear and 1/2 the back lash.
