The German adpositions are predominantly prepositions, with some cases such as entlang that can be used both as a preposition and a postposition.
are there any adposition in German that are used only as postpositions?
This source is pretty comprehensive... according to it, the post-onlys are
"halber" and "zuliebe"
... I would add "zufolge" to that list but Wikipedia disagrees. Still sounds weird to me when before a noun.