In "Maiko Haaaan!!!", a bridge going over Yumekawa (a fictional river in Kyoto) apparently has "夢ノ橋" written on it, rather than "夢の橋". I had two theories about why that may be the case. One was that it was the name of something, and therefore might have different rules than normal Japanese, and the other was that the bridge was supposed to be old, and therefore the name was written in a Japanese different to what exists today.
I checked "When is the katakana form of wo (ヲ) used?", and this answer seemed the best match to the circumstances:
The use of katakana ヲ is quite rare indeed; as you surmise, the use as a particle is Hiragana in modern Japanese. In older dialects, Katakana was used for particles as well, however, and you can see ヲ in use there. In modern times, it's also occasionally used for ironic or stylistic purposes, such as in ヲタク.
Was の one of the particles that was sometimes written in katakana?