I tend to buy a packet of mealworms (dead and dried) from Tesco or Asda supermarkets but they are available from pet shops and online. I just keep them in a tub with a lid and take out what I need daily. I have a chinese female hamster and I half the mealworms on two and hand feed them as treats!
She absolutely loves them. My syrian does`nt care for them at all though.
I get through about four mealworms a day (all halved in two) to make them go further! I don`t actually know what the full protein content is in each mealworm but obviously, they need to be monitored in older hamsters that may not need high protein in their diet. It really depends on the individual hamster and whether they have identified kidney issues.