Would allowing them to pay to have stands count as sponsorship? They could simply be advertising the products we all buy anyway. It would allow us to see some great demo's and maybe get some meet-day special deals?
Just an idea.
....What, like a mini GTI International Show?
I don't think that many aftermarket supply businesses wouldn't be very interested unless they could rely on sufficient business income from the event. Believe me, it's not an easy task getting everyone to agree a meeting place and a commitment to attend, let alone everything else.
But, I think it's worthwhile contacting a few circuit owners to see what the deal would be for a private club meet with track access.