I too am 6"5" and 270# and have no problem finding hose of proper length. I particularly like the piper's hose in various colors from ScottishLion.com, as they have a double or triple roll over popcorn top, are mostly wool (except for pure white), and come generously sized. Not least of all they are not very expensive---around $22 a pair (with free shipping over $100 purchased). Have a ball.

Also, Scotweb has what they call country socks (a bit hard to find on their website) which are very long and have some very colorfull turnover tops with various patterns. A bit more expensive but truly attractive, if the colors match well with your kilt.