Has anyone ever heard of phrases like, 'he came 'a riding?' More information? Quick 10 points?

These "a" prefixes before verbs are an old colloquial form that could sometimes intensify the action of the verb but was sometimes just a habit that didn't mean anything in particular.

The site below offers a discussion of the subject:

Edit: You occasionally see this in poetry and music because the "a" adds a syllable that improves meter.

I tried to find you an on-line explanation, but no luck.

Putting "a" in front of a verb (like"a-riding" or "a-going") is an American dialect form that arose from people wanting to put a vowel between two consonants when talking informally. "He's a-riding his horse" is easier to pronounce than "He's riding his horse." Adding the "a" has nothing to do with the artice "a." Adding the "a" was especially common in the American Southwest, because Spanish speakers aren't used to having as many words beginning and ending in consonants as English speakers.

Yes, it's just a dialect form. You also find it a lot in songs because it gives you an extra syllable for free. If you know Bob Dylan's 'The Times are a-Changing' try singing it without the 'a' and you'll see what I mean.

It's only an American thing, however, as far as I know.