Well like probably all people I'm full of every type of Elixirs (thousands of em) and haven't got a single red one yet. So maybe why don't you, guys, thing about some sort of Sacrificial of Elixirs in order to get red one?
1st idea I got is : Sacrifice 1000 green for 10 red, 800 blue for 10 red, 600 purple for 10 red, 4-500 yellow for 10 red
Sacrifice some amount of Elixirs (200-300-500 etc.) to get a random reward, among which will be a chance for red Elixir.