I'm sorry if this is somewhere but I'm having trouble tracking this information down.  Is Cardhalla going to be at GenCon 2019?  If so, can anyone point me to an email address or the like for someone I can contact about it?

Not sure if this helps you, but yes, Cardhalla will be there.  It is listed as an event in the catalog - or the destruction part is, anyway.  I don't see any contact info on that entry, though.

https://www.gencon.com/events/152249

That is actually super helpful!  I'll track it down from there.

Could you let me know what you find out?  I have a big box of cards that I can donate.

If you have cards to donate, just drop them off at the con. 

Yep, the official method (such as it is) is to donate on-site when there are people building.