I can't tell the difference between a well-tuned Chinese nib and a Jowo or Bock nib. But some people get hot under the collar when it comes to nibs - I put it down to snobbery but I could be wrong ...
If you are going to stock nibs, Phil, you will need to make sure that they are premium items. From that I would offer as a deduction that you should rather buy than produce. My reasoning is that if you are going to produce, (1) you'll probably get it done in China, and (2) you won't have an established brand viewed as 'premium'. Both of those being true, why swap an included Chinese IPG for YOUR Chinese IPG? One exception to this is Noodlers, but I'm not sure it would be that easy to emulate their success.
I don't think Bock have a dedicated reseller here in the UK, because I have to buy mine from Starbond-Europa who are extremely difficult to work with, So my vote would be for you to approach Bock about reselling their nibs here in the UK. But I don't doubt that they will never fly off your shelves ...