I have my Jayhawk about 85% done ( for the past 6-7 years, lol ), should be getting to it sometime....

Don't have the kit right here at the apartment ( stashed with the bulk of my stuff at my dad's shop ), but ,iirc, that's 2.5" dia ??

I recall seeing al those cones on Ebay , and did score one lot myself, but no 2.5" - two 3" including the Pro Patriot cone I will be using for a nice clone, and a 4" Patriot cone (short ogive), also got a third cone, another 3" OD, longer than the Patriot cone.

You might be able to turn up a partial or busted up Maqxi-Force or Impulse kit, if that's the same dia as the Jayhawk cone ? - although would not have th emolded -in bases for the antennae.

if you;re mising the fins, and the cone, doesn't sound like you got much of the kit, other than the decals and the vacuum farmed parts - if it were me ( and building it as a nice, flyable, bird - as opposed to a 'collector item' ) - I'd grab some LOC 3" tubing and cone, get the fin patterns from someone,a nd use the vacu-form pieces and decals, the .1" OD difference should not show up enough to look out of place, or affect decal palcement, I don;t think .
( will see if I can help with fin patterns , but mine's builtup, so would have to trace em :-(

~ AL