I've looked into this several times in the past. It seems one should look for a copy of the cartoon without the revised audio. I'm thinking maybe a copy could have made it to a european country with the habit of subtitling english movies rather than dubbing them, say like the Nederlands. In that case the audio track would be intact, but you'd have to look through hundreds of 8mm collectors.

If I understand correctly, what you're proposing is for somebody here to dub the line back in, that is, to re-record it from scratch? That wouldn't be the original though. Also, even if you find someone that can approximate a decent Billy Bletcher impression while doing a stereotypical jewish accent... let's be honest some would find that.... eehhhhhhh.