Styleforum.net is a good place to sell used men clothes. Go to the classifieds forum for classic menswear section and you can see a lot of similar items for sale. The people on Styleforum recommend selling on eBay too. There is even a member who has a business taking consignments and selling them on eBay for them. That might be the way for you to go.
http://www.styleforum.net/f/6714/classic-menswear-classifieds
42 Long is a popular size. There is a snobbery toward regular label Hugo Boss on Styleforum, but the higher level labels are well regarded. I don't know enough to know what you have but it sounds nice. You should be able to sell it without too much trouble. Just go into the main forum section and ask how to go about selling it and what's it worth. People will tell you.