This is a V-ring seal, Type VA, in the diagram #5 & #7. These are 50mm inside diameter for the 1500cc cars front and rear and 45mm inside diameter on 1300cc cars and Lancia Scorpion front, 50mm rear. These work as an extra dirt, water and etc seal for the wheel bearings. It is possible to not install them when replacing wheel bearings, I don't recommend doing this as the wheel bearing while sealed, they are not that well sealed against water and etc.
These are industry standard parts and should not be that difficult to get. NBR would be the correct seal material. While on might be tempted to consider Viton, this material does not have very good abrasion resistance and might not last as long. Companies like
and other similar industrial bearing suppliers sell them, check your local industrial bearing supplier