Purple sweets: where to get it

Source	Quantity	Chance per roll
Casket (CS Week) []	2–27	Common
Casket (CS Week) []	11	Common
Giant Oyster []	2–27	Common
Gift of Giving (active) []	1	Unknown
Holiday reward casket [{'content': '1/19 if less than 200 holy biscuits are owned. Otherwise, 2/19.'}]	7–15	1/19
Philipe's sweets []	5	Always
Reward casket (easy) [{'content': '1/16 if less than 200 holy biscuits are owned. Otherwise, 2/16.'}]	2–5	1/16
Reward casket (elite) [{'content': '1/19 if less than 200 holy biscuits are owned. Otherwise, 2/19.'}]	12–26	1/19
Reward casket (hard) [{'content': '1/19 if less than 200 holy biscuits are owned. Otherwise, 2/19.'}]	7–15	1/19
Reward casket (master) [{'content': '1/17 if less than 200 holy biscuits are owned. Otherwise, 2/17.'}]	15–29	1/17
Reward casket (medium) [{'content': '1/16 if less than 200 holy biscuits are owned. Otherwise, 2/16.'}]	4–10	1/16
Sandy Casket []	7	Unknown
Sandy Casket (red) []	7	Unknown
Security casket (CS Week) []	11	Common
Security casket (CS Week) []	7	Unknown
Snow impling (2012 Christmas event) []	1	Unknown
Treasure turtle []	2–27	Common