There are other bugs which suggest sys-kernel/linux-headers-2.4.19.ebuild is already available (bug#1497, bug#1453), but I have not seen it. I built this because gentoo-sources is broken (bug#6787) and I wanted headers to match the vanilla-sources-2.4.19 I was installing. In order to construct sys-kernel/linux-headers-2.4.19 from sys-kernel/linux-headers-2.4.18-r2 I only had to change three things as can be seen in the patch file I will include. The only change of importance is the last one in which I added a check for the properly named unpack directory instead of moving the wrongly named directory to the rightly named directory.
Created attachment 3240 [details, diff] sys-kernel/linux-headers-2.4.19 patch from 2.4.18-r2 This is the patch to constuct a working sys-kernel/linux-headers-2.4.19.ebuild from sys-kernel/linux-headers-2.4.18-r2.ebuild.
One of the bugs I cited was incorrect. It should be bug#1543 not bug#1453.
in portage, please test and such...