I bought ours from our vet -- I am not sure if stores carry it, unless they have a vet associated with them. I would call around a few vets in your area and ask who has it, and cost. I think I paid more than necessary for it, not sure what normal is -- ours was $14 for a pouch of the fine-grind Critical Care. It is a powder, you mix it 3:1 water/CC -- then we add a dab of babyfood or pureed fresh fruit to help the flavor.
When you mix it, that portion will keep for 24 hours in the fridge, we heat it for 8 seconds in the microwave to take the chill off. Mix small portions at a time, like a teaspoon of CC & 3 teaspoons of hot water. That way you won't have waste. Then use the needle-free-syringe to feed.
It has the D3, the calcium, B12, etc that may boost his system a little and make him feel better, more energized. Sometimes B12 is a deficiency, and can help energize. A lot of people on the boards use CC to nurse their beardie back to health, or maintain for short periods of hunger-strikes. It would replace the babyfood you're feeding now.
Do you have a mercury-vapor UVB? Or is it the strip type lite? I am wondering if the UVB levels have dropped, and he's not getting the D3 synthesis that is so important to them? Have you tried to take him outside to get a boost of sunlight? Maybe a test to see if that will perk him up? We usually hold ours on our chest, and pet them to keep them calm, and they perk up wonderfully with the real sun. No substitute for the real thing :mrgreen: it might be worth a quick try?