V-Belt Global Supply.http://www.vbeltsupply.com/
Should be a 5/8" x 97" belt for your 42" deck.
V-Belt Global is the best place I have found to get quality belts.
If you want a Kevlar belt search for part #B94K
I have found that Brush Hog belts last longer than anything else on my GTH2754 and I can get them quicker and for half of what a single OEM Husqvarna belt cost.. Best part V-Belts gets them to me quicker than the dealer.