RockAuto has them too. They are cogged, which makes them much more flexible than the solid belts and hence easier to install. And yet you will probably still have to pry a little to get it over the generator pulley. The problem with using a longer belt is that then there isn't enough adjustment to pull it tight. The good news is that they seem to last much longer than the solid belts, so don't need to be changed as often.
Make sure to firmly tighten the lower generator bolts AFTER adjusting the belt (as well as the upper of course). If you leave them loose enough to pry the generator around (which is how I used to do it on other cars), the front bolt will work loose and ruin both the generator and the front mount. BTDT
Also a good idea to replace the Nyloc nut(s) every time IMO. They lose some of their holding power with each install/remove cycle. I've actually switched to using all-metal 'Stover' nuts, because they lock more positively, are not affected by heat, and generally don't have to be replaced every time (though aircraft manuals still say they should be).