Throughout the Shadowlands, Inamorata (Unredeemed use these) and Sacrosanct (Redeemed use these and also listed in the items database as Sancrosanct) weapons drop from sided mobs that can be upgraded in a two stage process. If you wish to, you can just upgrade via the first process by adding Grey Glyphs - but the benefits from upgrading with the Turn Spirit as well could be something you are interested in. This guide looks just at the initial upgrade with a grey glyph.
To get your hands on the weapon you want, you have to hunt sided mobs. Unredeemed mobs drop the redeemed weapons - and vise versa. Unfortunately their drop rates are not fantastic (although it always feels slow when you are trying to get something you want!!) and also, you will need to venture further up in the Shadowlands depending on the QL you are looking for.
For the first upgrade to the weapons, you need to add a grey glyph. Most glyphs can only be applied to particular weapons - and also just 1 glyph can be applied so make sure you choose carefully what you want to to upgrade with.