In Icelandic, there are four verbs that are descendants of reduplicating verbs: they're called the "-ri" verbs due to their characteristic past tense suffix that they share with no other verb. These are "snúa" (to turn), "núa" (to rub), "gróa" (to heal) and "róa" (to row). In Old Norse, the verb "sá" (to sow) used to be in this group but Icelandic changed it to a weak verb (its past tense is "sáði" instead of expected "seri").
These four verbs come from Proto-Germanic strong verbs. These verbs are currently (infinitive and first person past):
- snúa > sneri
- núa > neri
- gróa > greri
- róa > reri
- (sá > *seri)
Of these, the interesting ones are the actual reduplicating ones, "snúa", "róa", "gróa" and "sá". These used to be quite different in Proto-Germanic:
- snōaną > snúa
- rōaną > róa
- grōaną > gróa
- sēaną > sá
In Proto-Germanic, they formed their past tense by reduplication of the first syllable, with other changes as appropriate of strong verbs:
- snōaną > *se-snō > seznō
- rōaną > *re-rō > rerō
- grōaną > *ge-grō > gegrō
- sēaną > *se-sō > sezō
Due to Verner's law, the /s/ in those past tenses changed to a /z/, which then merged with /r/ in Icelandic. In "snōaną" and "grōaną" there was an additional metathesis (to "snezō" and "gregō"), and "grōaną" itself analogically probably aligned with "snōaną" to give "grezō". I'm not aware of any other such reduplication in Germanic languages; Icelandic's closest relative, Faroese, has already analogically levelled these reduplicative forms and made these verbs fully weak.
As for "núa" I am not certain what had happened before it became a "-ri" verb. I cannot find etymological information for it in the dictionaries I use, but it might have been "nōaną" that formed its past tense as "nenō". How it became a "-ri" verb is something I don't know but I suspect it underwent the same analogy as "grōaną" did from "gregō" to "grezō" ("nenō" > "nezō").
The Western Germanic "ge-" prefix doesn't have anything to do with reduplication as it comes from Proto-Germanic "ga-" which itself comes from Proto-Indo-European "ḱom" (whence also Slavic "сън" and Persian "ham".) The reason it became a past participle marker is that it became added onto verbs to show the perfective aspect/a completed action, and then was spread out to the past in general. Verbs prefixed with PGmc. "ga-" always took on some suffixes that made them nouns or adjectives.