Every year I never know if I’ll be able to make GenCon, by the time we know the True Dungeon is always sold out so we’ve never been able to try it. 

Is there any chance that there are random openings for a couple that just walks up?

There’s 1 available ticket now which is a bummer, I was so close haha
 

Yes, there is a chance—depending on the time.

Be sure to check the True Dungeon forums as well.  Some people buy full runs so they can control the party difficulty level.

https://truedungeon.com/forum?view=topic&catid=736&id=257573

There are currently a couple of groups looking for more (LFM) for The Golden Obelisk dungeon (the intro dungeon).  This dungeon will be perfect for people that have never played before.  It is a little shorter (and therefore cheaper) and it is a sealed pack dungeon so you will be equipped just as well as all the other players.

There are also a couple of groups LFM for the Tomb of Tower Redux.  This is a full 2 hour dungeon, but is also sealed pack format, so again good for new players.  One caution - one group wants to run Tomb on Hardcore difficulty, which will probably be tough in sealed pack format.  I recommend avoiding that one if another option also fits your schedule.

Good luck finding tickets.