ideas for creative solutions to combine members, services and digital download in one package

Hi,
We are non profit creating a visual campaign for companies and organisations to use on their own platforms.

Companies and organisations sign up to join the campaign. When they sign up the choose an animal, they would like to sponsor. Each animal can only get chosen by a maximum of 5 companies/organisations. We have 40 animals to choose from.  

We are trying to figure out how to best set this up in squarespace. The easy solution would be a digital product for each animal, but our challenge is, that the downloadable assets will not be ready for download by the time they sign up to join the campaign. So this solution will not work. 

We looked into a service product, but we don't see an option to upload files there either.

We then looked into membership areas, which might do the trick, as we can then create a member area and use email campaigns to notify the companies when the downloadable are there. But it looks like we will then have to create a distinct members area for each animal because all companies otherwise will have access to all assets for all animals. The biggest members area plan, we could see, was 10 distinct areas, so we can't create 40. 

Can anyone help us identify a solution, where we can have people sign up and then somehow allow them to return a few weeks later and download the assets without giving the access to other assets than the one they signed up for? 

Thank you in advance!