Oreilly auto and other auto parts have them. Kaman had a a bigger selection of various lengths. I still had to use an adjustable diameter pulley and it wears down as it is aluminum. To get a cast iron one like it may be a bit costly. For about 15 dollars at Granger near by store I got another. If you use a belt it would be best to get a wide belt (Not 4L) and clutch to match. Synchronous pulleys are expensive so if I made another build I would try to do all with chain.
These are not cogs that fit in synchronous pulleys, they just bend easier around small diameter v-belt pulleys. Too small a pulley under about 3 inches get to be not useful for the power used and even with a cogged belt it does not matter. I found that out by experimentation.