For the dealers, don't think so since they give their cards/details freely. If you ask for the emails/contact details of those who signed up, that's more like breach of privacy.
But it is conflict of interest for the girl if she's obligated to not provide the dealer info if the original organiser deems you as competition. But if they are no longer organising fairs in the future or banned from the hall, then it should be ok.
Yeah, i could see why they would be unwilling. But it shouldn't hurt to ask.