You got :
Ralph Lauren upto 56"
Calvin Klein upto similar size.
Paul & Shark upto similar size.
Zegna upto similar size.
Pierre Cardin upto 54".
Yoropiko upto 44".
Evisu upto 44".
Gucci similar size (I seen them 44/46").
Versace similar size.
I seem to remember Sugar Cane did a 60" pair as a 'promotional item' so they can go BIG!!!
As for length they probably go upto like 38" or 40" leg!!!!
Exactly what size do you need (waist x leg)?
Take a look on :
Rochester Big & Tall Men's Clothing and Accessories (its US but the prices are pretty much what they say but in £s rather than $!!)
They have a large store in Knightsbridge opposite Harrods.
Went there today (got their sale on at mo) and saw 'Dawn' (Tara Toninton) from EastEnders going into a shop near there. I had a bit of 'I recognise you from somewhere'

. I think I'm in

.