I'm a Mom with a son who is much like you. You will have to have a suit custom made by a Taylor. There are men's specialty stores that can help you. It will cost more (sorry, we found this out when we tried helping our son buy his first suit last year). Good Luck!
I understand your frustrations, our son is 6 ft.6 1/2 inches tall and only weighs 143 lbs...a little bit more than you, but his waist is very thin. I know how to sew, and have always been able to alter his clothes, however, he is on his own now. He seldom brings me "clothing" alteration problems today, I think he's found some places to find clothing that fit properly...keep looking! You're not alone....though you stand above the crowds, like my son.

I have also found that amazon.com if you do a search for the size cloths you need. My son is 30 x 38's they have them they are a little more pricy than usual at JcPenny my hubby pays about $30 for a pair of pants, I found my son a pair on amazon.com over christmas that cost me about $50, sometimes they are less, but not usually. Custom Taylors are always great, but even more costly. We are in southern AZ so he has 1-2 pair pants but mostly wears shorts, as you can take a pair of pants and convert it to long shorts easier.

I have been also experimenting with taking 2 pair of the same pants and cutting the legs off 1 and adding it to the other pair. Its ok but the pants kind of need to be cargo pants, and you need to cut the fabric at an angle as not to look too weird.