Card upgrade clues have the potential only to drop from reward coffers (like winning/losing a match or turning in a ToT daily). Without the clue card, the upgrade will not populate in those spots.

Queue does seem long at times. I assume due to low population of people playing.

Yes, you are likely being matched with people who have been playing longer than one weekend. It’s a grind to rank up. If you go to collectibles and look at each patron, it tells you how to unlock the other decks. Usually involves collecting deck fragments that drop from various places/things (like vents on High Isle, etc).

I have never had to wait hours. It does seem to matter what time of day you queue, you're more likely to find a PVP match during peak times.

Tribute has been out for a while, so there's less new players in the queue. As others have stated, I would recommend sharpening you skills against the NPCs before entering queue. You can still get clues from npc match coffers.