i have some 6 inch lava elc patch cables but need some that are longer maybe a few 9 and 12 inch ones. But they are not available in the U.K. unless I purchase the kit which I don't trust myself with figuring out.

Is it normal to use two different brands of patch cable? If so what would go well with the lava elc? I was looking at the Gotham ultra pro as apparently they are from lava and are available in bigger sizes here on Amazon.
It really doesn't matter at all if you mix brands of cable.  As long as they are all of good quality it will be fine.