A picture could certainly only help, but curious if It is a quick release, or a full threaded pin? Some of them just use a standard 5/16-18, but off the top of my head I'm not sure what the thread pattern for the QR knock off is. I've never had to match a shaft to one, so never had that need to know.
Like KJ mentioned Your intent in knowing may help with answers, because if Your looking to have a shaft made or matched to It, and It's a knock off QR, then You may also have the option of changing the pin. As well as solving the bastard thread count issue, changing the pin can also give the option to center It better then It may now be centered, and that may help with matching the shaft up. Some of those imports have pins that are not centered to perfection, I'm not saying this is a issue with everyone, but It is an issue that plagues them never the less, and sometimes changing the pin provides a much cleaner base to match with the new shaft. Less headaches matching the faces to get the cue to roll true as well.
BTW, I use to sell J&J cues, and if You only need a stock shaft then they can Probably sell You one, They usually have replacements for sale. If however your looking to sink some money into a custom shaft, then the above may be something to consider.