The belt is an odd-sized T-belt (timing belt), the odds of you finding the exact same size at an auto parts store is very slim.
Just about anyone who sells a 4G should also sell belts for it. This is a slow time tho, many places are out of stock of parts. You might try calling Helio to see if they can sell you a belt for that 100T pulley. Their number is on the Contact page.
Hey, shwnrttr I just happened to find a source for these belts. The company is called VBeltSupply.com-PH:888-291-5450. I bought one from them and it is the exact match to the china belt. Belt No. 505-5M-15 Synchronous Timing Belt,cost me $18.62 shipping included. Good luck!