drive belt idler

I made the assumption (we all know what happens when one does that) that
timing belts could be ordered in any length when in actuality there are
"industry standards" in lengths. Sometimes with a several tooth jump in
length.

With this assumption I made my mounting bracket for my servo motor. The
belts available in the adjustment range I have are either too small or too
long. I can redo the mount but don't particularily want to. I was thinking
of going with the longer belt and adding an idler pulley to take up the
slack and help keep the longish belt from possible vibration.

Now the question. I can't seem to find a smallish idler pulley for a HTD
15mm belt. I am looking for about a 1.5" dia pulley. Any ideas?

Thanks,

Thomas