George - Speaking only for myself, since others HATE it when I speak for them
, when it comes to fountain pen sales, the pen grabs the attention and the nib often makes or breaks the sale. In general, nibs cannot be acquired from specialty vendors as they are most often specific to the pen. That being said, nibs can be acquired and custom fit to pens, but the cost is considerable, sometimes equalling the cost of the nib itself.
I have not done craft shows, but I would expect there would be less numbers of discriminating buyers than at pen shows. In general, there will be far few numbers of fountain pen users looking for a "Broad, semi-flex nib". In fact, my experience indicates that nib requests break down this way. Medium/standard and fine/standard account for approximately 90%. All others account for a total of about 10%. Those who require specialty nibs generally know how and where to get the nib they require fitted to their pen of choice.
In terms of the flex of the nib, that is normally controlled by the manufacturer. Certain pens come with a super flex nib, like the Pilot/Namiki Falcon. Certain Sailor pens come standard with a double broad or music nib. Expert nib meisters can adjust many different nibs to write like the specialty nibs, but at a price. My choice of nibmeisters is Richard Binder, but there are many other talented grinders.
The steel nibs that come as standard with our component kits are generally stiff to semi-flex. The beauty of these nibs is that an inexperienced user will not destroy the nib with the first use. The disadvantage is that the nib allows of very little control over the line.
Overall I think you will be well-prepared if you carry combinations of nibs to cover semi-flex and standard flex, steel and gold, medium and fine tips. That's still a lot of territory, but fountain pen buyers understand this and are generally more willing to pay a premium over a rollerball based on the advantages of multiple fountain pen nibs.
