I have a Toro commercial mower I bought used recently. The deck was missing a v-belt. Apparently the mower deck I have had very low sales so nobody makes a third party belt for it. I could only get the belt directly from Toro.
I paid $60 for the belt from Toro. For some reason, Toro included the profile and length of the belt on the part when I got it. I could have purchased the same belt for between $10 and $15 if I had known the length and profile. I willing paid the $60 so I'm not feeling totally ripped off. At least other belts do have third party replacements available.