I searched google, jisho, and yahoo. I couldn't find a proper pronunciation for 初商業誌.
It's read as はつしょうぎょうし.
You can never find it in dictionaries because it's actually three words:
- 初【はつ】: first (jisho.org)
- 商業誌【しょうぎょうし】: commercial book/magazine (often as opposed to dōjinshi)
初商業誌 is typically used when a dōjin manga-ka makes a debut on a magazine available in the commercial market.
Just ask Google translate to detect the language, then hit 'Translate'. Google translate can be pretty sucky from time to time so don't treat it as gospel, but use it as a translation aid:
"The first commercial magazine"