なら is for nouns (and な adjectives by extension), but it has a verb/adjective equivalent ~たら where the た is the end of the past tense of the verb or adjective.
なら and ~たら generally refers to conditions in the past, though I’ve seen it used in cases where I suspect it was not for past conditions.
I believe ば can be used on nouns by using the verb である since it is the original form of だ. It would become であれば.
I don’t know enough to determine what the reason for that could be. It doesn’t fit neatly in my mental framework of Japanese. Are you sure it wasn’t like this in the original source?
旅行に行くの なら
Another possibility is that it’s a colloquial expression and it’s not technically grammatically correct.
Of course, there’s also a high possibility that I just don’t understand it well enough.