1. If you click on the user silversmurf's profile, he has the percent chance of getting a Hakkon from dragons and the store. Basically you gave to defeat nightmare or heartbreaker dragons for a chance at them. You have a 15% chance to get your first, then every one after that cuts the chance in about half so approximately 7, 3, 2, 1, 1% to get your 2nd, 3rd, 4th, 5th, and 6th. Many users have had horribly unlikely luck at getting them. Some didn't get the first until 180 dragons and some get them after only a few. The percent chance shouldn't be taken as law based on some people's experiences. You can also get them from the store chests assuming you have a certain 'loot score'. I am not sure this is retroactive but if it is, you should be fine based on your prestige. The percent is supposedly 1% to get a Hakkon out of a store chest I believe if the loot score is at the correct level. There are a lot of other threads with more details on Hakkons if you search the forums. But do it quick since the forums are closing kind of soon.
2. Soloing Heartbreaker requires quite a lot of promotions and good gear. It's not really intended for that although some people have done it. Heartbreaker isn't too bad if you have a Saarebas support mage spamming barrier, rings, applying glyphs, etc while other players focus on damage. Heartbreaker enemies have all different abilities, extra guard and barrier, a huge health pool, the most annoying enemy in gaming history, the semi-invulnerable Venatori Mage, and the red templars even have an attack to turn on friendly fire briefly... The final wave has you battling 6 or so Commanders at once. I'm personally not super excited about Heartbreaker since it doesn't give you better rewards than NM in terms of XP or Hakkon chance but it definitely provides a challenge. And you are correct, people generally aren't joining or starting heartbreaker matches that often because it definitely requires a coordinated team or high level players.