The adverb 'ahold' is an Americanism that exists entirely in orthography. Most English speakers will recognize the construct "get a hold of"; in America, it is normal to write this as "get ahold of".
This has become so common that Merriam-Webster.com, Cambridge Dictionary, Macmillan Dictionary, and American Heritage Dictionary all have this definition as their primary definition; Wiktionary relegates it to the second definition (under the traditional, and archaic, definition of keeping a ship held steady into the wind while sailing out from shore), and the Oxford English Dictionary only recognizes it as "a-hold", identifying it as a dialectal or colloquial form.
Most guides to formal writing will advise using "a hold", but this is more and more a tip of the hat to international readers, and not something that most Americans would notice.
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