You won't find them at the Auto Part Chain Stores.
If you want made in the USA you will have to look through the threads as someone posted a source:
DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum
PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles
There is a bunch of them on Ebay; likely Asian made unless the Ad states US Made. However, you need to know what type of Seals are in your Tubro Charger as the Garrett t-3, t03 turbos had more then a couple types of seals.
It is also possible that a local Speed Shop might be able to supply a kit (there should be a Plate with the Model and Part numbers on it). Likely Asian made but could be US or original garrett parts.
The reason a speed shop might have them is that the T3,T03 and even the T04 (same Bearings and maybe the Seals) Turbos have been used on all kinds of Gas Cars. This is where the different seal issues really comes in.