Tetenal still makes the 3bath E6 in 1l size, itīs available in Germany. Itīs probably just your national distributor who is vary to sell it.... tell them that you want it, and that may change.
Look, there is the listing in a german mailorder house:
OTOH, the 5l kit version costs slightly more than double the money (77EUR) they ask for the 1l kit (34EUR). Even if you donīt use it up, you may end up saving some bucks... I know that once the seal is broken the chemistry lasts some 14months, a lot longer than most other kits available on the market.