Hi Kato, I'm relativlely a newbie too, and also
would like to build the '12' or L15 Seas Zaph design.
But don't know where to source the drivers in AU!

Re: your Q, Mr JK (either somewhere in his site or
maybe in www.diyaudio.com - 'zaph new design' post I think) suggested unwinding a 1.8mH and described how
to use the 'Lalena inductor calculator' to work out
how many turns to remove. Or, alternatively you could
buy a cheap eg $30AU inductance multimeter and measure.
Probably best to use the specified inductance values and also the specified DC RES. of them.
Hope this helps, good luck with your project, let me know how the finished version sounds please? Grant