All refill package henna brow hair dye colors are sold in 5gr refill bags (around 40 treatments, if you stick to the size requirements) The colors are available in blond, light brown, medium brown, dark brown, grey and black. You can fill these bags with the glass jars that you have already ordered or you can buy this separately. 
The henna should be mixed with (warm) water, so you do not have unnecessary costs for mixing products.