Why not rear your own meal worms. I do, and it's very easy. They can be expensive to buy and my hens love them.
1. Get a plastic tub or a container. Inexpensive clear containers with vented snap on lids are available at pet stores. (I use a vivarium/aquarium type container)
2. Place 1-2 inches of substrate (which mealworms will eat) in bottom. Use bran, oats or a mixture of the two.
3. Place 1/2 a potato/apple/carrot on substrate or in a small dish (supplies moisture and food).
4. Get around 2 dozen mealworms from the pet store.
5. Place mealworms in container, which should be kept relatively warm.
6. Replace potato/apple/carrot every couple of days (do not let it get mouldy).
7. The mealworms are the larval stage; within 3 weeks they should pupate, then in another two weeks beetles should emerge.
8. The beetles will lay eggs, which are minuscule and very difficult to see. When these hatch, the larvae are also very small.
9. The beetles will die, while the larvae will grow and repeat the cycle.
10. After one life cycle the colony should be well established and you can start using them for treats/food.
11. Once feeding mealworms from the colony, you can offer a variety of vegetables and fruit (e.g. carrots, orange, greens) to increase the nutritional value of mealworms for your birds.
12. Do not allow mould to grow on the food or substrate.
13. Add bran/oats as necessary to maintain the substrate level. Start with fresh substrate occasionally (especially if mould or damp conditions develop).
14. If you have too many mealworms, place the whole container in the fridge, as this will stop their development.
15. Simply rewarm to room temperature when ready, and the colony will resume development.
Tips:
1. Do not change the substrate until the colony is well-established, as eggs and tiny larvae will be lost and the cycle interrupted.
2. Once you have lots of mealworms, it is fine to completely clean out the substrate - filter out the mealworms, discard the substrate, and start over.