most speakers do not have published impedance curves. however all drivers do. sometimes you can find the parameters for the drivers of pre-built speakers, but usually not unfortunately. most impedance plots of woofers have somewhere in the 100-200hz up to usually 800hz to 1khz in the “nominal impedance” range. IE an 8 ohm woofer will typically run roughly 8 ohms in that range. usually a dip, followed by a huge impedance spike at around 100hz for 20-30hz that then drops waaaaaaaaaaay off to as low as 1ohm or less. on the other end, it usually rises like a roller coasters first hill till it hits 60+ ohms at the far end of the woofers limit.
tweeters do the same thing, but at higher ranges. the low end dip and rise varies typically a lot more as tweeters resonant frequency(ie as low as it can go) vary a ton.
xover values and design can and will effect the impedance plot as well.
random image quick find on adding a resistor and how it effects the impedance plot
unless the manufacturer randomly posts the plots(unlikely) you have to measure yourself. same goes for DIY projects.