Try TK Maxx if you have one near you.

Or if you have a designer outlet near you see if the ralph lauren stoe has a big section - the one at biscester goes up to whale size.

I'm not being harsh but if he is a 44-46 waist he needs to lose weight. Its amazing what you can do in a year - I've done 4.5 stone so far this year. Its worth the graft.