I suspect what you need are long clothes. I often find the xxxl clothes are for really fat people. JKs idea is a good one.
In the past few years I ( 6ft 4) have had luck with Henry Loyd and Musto.
I have also been very fortunate in being able to get multiple purchases in Holland where they appreciate the situation with tall people.
Watch out for Dubarry who do an extra long sea boot. The extra height in the boot compensates for the lack of length in the leg.
the high and mighty shop in Knightsbridge might also be able to give you some pointers.
best of luck.
Take it easy ....but, take it all the way.