Question on Identifying an IP range of a specific location

Hello! Disclosure: New here, and a noob but i did read the rules!

So here's the scoop:

I'm wondering what the best way to determine an IP range at a specific location, where an upcoming tradeshow will be held. We are trying to provide attendees with free access to our web service via an autologin based on IP of the wifi service at the venue.

Is this possible?

Happy to provide extra info! Thanks in advance!