yea you can pick some up from scott at fi.
i will warn you though, as i just did it today...
if you are going to completely replace all the tinsels (meaning going under the dust cap)
1) be VERY careful removing the CA glue coving the solder joint. you can easily cut through, or bend the coil wire enough so that it snaps where it connects to the coil assembly
2) do not desolder the connection but rather, just cut off the tinsel leaving about 1 or 2 mm. solder the new tinsel to that point. if you desolder the joint and seperate the coil wire from the tinsel you will see that the coil wire is all coated still and the solder will be a major PITA to get to stick to it
3) dont get anything in the gap
i ****ing hacked up my BTL pretty bad as this was my first time doing it. i WAS going to make a tutorial, but it just went to hell, so i gave up. i got it working and shit, but i had some major issues like breaking the coil wire. i had to pull some up off the coil assembly to solder the tinsel to, and then for some reason my coils were reading fine. then once i had the dustcap glued on, and tinsels soldered to the terminals, i was getting .7 at 1 terminal (which is normal for fi's 1 ohm coils) and 1.4 at the other. so i had to remove it and **** around some more.
lesson mother ****ing learnt. id ALMOST rather buy a recone.
heres a nice link. i believe the 18" xxx are a **** cone too, so thats a plus in this situation.
http://www.soundsolutionsaudio.com/forum/index.php?showtopic=8208&hl=tinsel%20lead&st=0