I think back in the early nineties, Parker Uk had a catalog with some 22 or 23, perhaps even 24 different nibs for some of their models, namelly the Duofold, the 75 and Premier and even the 45 .
I exchanged nibs directly with Newhaven - some F and M left oblique of two different degrees, because they weren’t available in my country - and bought a 14 k fine rigth oblique .
Later on, they told me that they sold the replacement nibs to pen dealers .
I don’t even dare to ask the price of that set of testers .