The member Rayban on here makes wonderful belts. I had him make me one almost a year ago and it has been great. Double layered, double stitched, 1/4" thick, nice and stiff, and for a pretty darn good price. Here is is website: http://www.rgleather.freehomepage.com/
I own 2 1.5" width 5.11 TDU belts.
They hold up well but they are not the "gunbelt" style.
For thick-lined belts, I'd check www.thebeltman.net and some of the custom shops; Milt Sparks, Mitch Rosen, Greg Kramer, Don Hume, Ken Null, Galco, Bulman Gunleather, El Paso Saddlery, Tex Shoemaker.
Larger firms like Blackhawk, 5.11 Tactical, Unkle Mike's, Safariland also have well made, sturdy gun-belts.