Using a Third-Party Mobile App to Gather Email List

I want to use Squarespace Email Marketing instead of MailChimp. I have used MailChimp for years. I also use their iPad app "MailChimp Subscribe". Currently, I use that app to gather names and emails at events. Then I take that list and download for Squarespace lists. 

Does anyone know of another app for the iPad that will do this and integrate into Squarespace Marketing?

Honestly it sounds like this maybe the best solution. There isn't really anything like this that will integrate with Squarespace campaigns.