Ruin Tokens are an alternative to get Ruin set. To buy a Ruin piece, you need 5 Medallions of Ruin.
To get a Medallion of Ruin, you need:
4x Shard of Ruin that drops from T4 white bags or
3x Fragment of Ruin that drops from T4 green bags or
2x Aspect of Ruins that drops from T4 blue bags or
1x Remnant of Ruin that drops from T4 purple bags
Once you have for example 4x Shard of Ruin, you can trade them for 1 Medallion of Ruin from vendors:
For Order: In Altdorf, at 32.5k 49k east of the War Quarter.
For Destruction: In The Inevitable City, at 22k 51k northwest of Pavilion of Slaanesh.
Note: These 4 tokens can not be mixed up. It means that you can not mix for example Shard of Ruin + Fragment of Ruin to get a Medallion of Ruin. Nevertheless, you can get 1 Medallion of Ruin trading Remnant of Ruin, and another one trading Shards of Ruin.