#1
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.
#2
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.