Selling vintage parts: when are prices highest?

Is there an annual cycle for price fluctuations for vintage parts? If so, whet are the best times to sell? When are the best times to buy?

For example, when do people look for parts for an Eroica bike? When do people buy Christmas gifts? When do they buy for a new outdoor cycling season?

I'm thinking about parts from the '70s and '80s.

Thanks.

(Mods: I am not asking for friend. If I decide to sell via BF, I'll be happy to sign up for a premium membership.)