Hi Niki. I'm in the UK and my favourite supplements are ones that you can dissolve in their drinking water (make sure you change it every day). The good all-round supplements that I keep in stock are Critical Care Formula and Reptoboost, both produced by Vetark.
CCF is an all-purpose nutritional supplement that's reptile-safe and you'll be able to get it from any vet. Reptoboost should be available from good reptile shops or is readily available from online suppliers. Reptoboost is a probiotic, which helps keep digestive gut flora up (necessary for the hatchling to properly digest anything that you manage to get it to eat).
I use alternate between the two when I get persistent non-feeding hatchlings and I reckon it can buy me an extra couple of months of trying to get them to eat of their own accord.
I wouldn't worry specifically about calcium unless the hatchlings are showing signs of skeletal deformities. My usual supplement for this is Zolcal-D (also Vetark), which contains the Vitamin D3 necessary for the snake to metabolise the extra calcium that it contains. This is given in the drinking water as well.