The A5 uses any ar10 adjustable tube.
Since you mentioned KAK, they sell tungsten buffer weights individually. A carbine=3 steel weights, H is 1 tungsten and 2 steel, H2 is two tungsten and so on. The A5 has 5 weights, they are sold as A5h0-A5h5.
Buy a few and you can tune it buy taking your buffer apart and trying different configurations
Sprinco sells springs, and sell "extra power" ones as well that are a bit stiffer. They're color coded, but I don't remember which is which. The green is the extra power rifle spring I use in my A5 setup.