It seems to me that other than the daily login rewards and the odd reward from finishing a Challenge/Mission of some kind in game, the only way to get free Sacreds is through NM or UNM clan boss.

Besides what is mentionned above there is also 3v3 arena which offers sacreds to Gold tier players. 

You would think they would have a good sale on sacreds going but i havent gotten any yet.

Lol is there a way to sign up for more special offers. :)

excuse me? this is false there is no 3v3 arena. this is from a moderator?? 

Why am I not able to play in the NM/UNM clan boss, I am allowed to play easy, normal and hard only ?

To  be  fair  i  have  been  doing  NM  clan  boss  for  over  a  month  now  and  havent  seen  a  sacred  shard,  they  maybe  dropping  in  UNM  but  NM  seems  veey  rare.  Other  than  that  getting  sacreds  outside  of  the  shop  is  difficult.  With  a  6%  chance  outside  of  a  x2  and  a  12%  chance  in  a  x2  you're  gonna  need  7-8  to  stand  a  decent  chance  of  getting  a  legendary.  To  get  that  many  you  either need  lots  of  patience  or  lots  of  money.  

It depends on your clan. Apparently your clan has never killed the Hard Clan Boss yet, so you can't do the Brutal CB until they do. Same for NM and UNM - you must have defeated the previous difficulty boss at least once to unlock them. 

So you may need to change clans to one that has unlocked the difficulty you want to hit. 

He obviously meant the Tag Team Arena - 3v3 as in three teams vs three teams. 

Are you getting the top chest? They do drop from NM top chest but indeed very rarely - probably less than once a month. From UNM top chest, it's still rare but you're likely to get a few per month, that's where most people get them from. Plus obviously login rewards, monthly rewards, campaign/faction war/doom tower rewards. 

yes,  i  get  the  top  chest  every  day.  i  have  had  1  leggo book,  1  epic  book  and  a  void  shard  in  the  last  6  4-5  weeks.  The  rest  has  been  potions,  brews  and  a  piece  of  gear  which  is  usually  trash.  

the  rng  is  crazy    my  clan  clears  unm  everyday     i  get  last  chest  x2  everyday       3  months  ago  i  got  8  sacreds  in  one  month    past  two  months  i  got  2  sacreds  2  voids  and  18  ancients  along  with  15  leg  books     Leggo  books  have  been  awesome    was  finaly  able  to  book  out  3  of  my  leggos  

if you finish all faction war bosses then you get a few of sacred shards.