Something tells me that those 7500 5* shards you have were the 5000 5* shards from last month's login calendar and the 2500 5* shards Kabam gave out as compensation recently. if you are in an ally that gets 5* shards from wars and SA, or if you are active enough by doing arenas and event quests (Heroic is an easy source of 5* shards), you would have those 10k 5* shards in no time.
If you don't get 5* shards from your ally, you can still grind for the remaining shards from arena and quests.
Comments
Monthly quest may be too hard at your level, but is probably the best way if you can
Alliance rewards are usually the easiest way?
Win 5 rows in a row and that's 2500 shards, a week and half - 2 weeks.
Still close, including arenas too.
If you don't get 5* shards from your ally, you can still grind for the remaining shards from arena and quests.