I'm not sure what you consider "rare" or how you sourced your parts, but I feel like maybe your timetable is a little off.
I can't speak to the economics side, but I feel fixed-gear mania was in full-swing well before 2006. I worked in a bike shop in a small Midwestern city (so presumably the trend had already been on the rise on the coasts well before this) from 2003 to 2005, and even then fixed-gear discussion was not infrequent. I'm pretty sure you could order flip-flop hubs from QBP at the time, although I can't recall if fixed-specific hubs were available, since I don't recall anyone ever actually wanting one and not a flip-flop. My point is that major suppliers were already providing new parts specifically for that market.
Although, yeah, I don't recall any non-boutique manufacturers making fixed or flip-flop models while I was in the business.
Anyway, maybe you specifically meant the secondhand or market, but I just wanted to point out that your LBS probably had plenty of fixed-gear parts available before '06.
You are correct about the parts being available in QBP and such. I was working in an LBS at the time. I suppose the timetable of 'boom' I'm talking about falls in when the generic sealed-bearing Velocity hubs started to show up on the scene. Before that you needed to go the Surly or Suzue Basic route if you wanted a cheap-ish hub. Prices were notably higher in price though.
I know that I was getting into things right around '03, and my friends were all about it by about then too. But it wasn't nearly as regular an occurance to see a fixie rider on the street (in SF/Oakland) until '06 or '07.
I can't speak to the economics side, but I feel fixed-gear mania was in full-swing well before 2006. I worked in a bike shop in a small Midwestern city (so presumably the trend had already been on the rise on the coasts well before this) from 2003 to 2005, and even then fixed-gear discussion was not infrequent. I'm pretty sure you could order flip-flop hubs from QBP at the time, although I can't recall if fixed-specific hubs were available, since I don't recall anyone ever actually wanting one and not a flip-flop. My point is that major suppliers were already providing new parts specifically for that market.
Although, yeah, I don't recall any non-boutique manufacturers making fixed or flip-flop models while I was in the business.
Anyway, maybe you specifically meant the secondhand or market, but I just wanted to point out that your LBS probably had plenty of fixed-gear parts available before '06.