DO not buy waste milk - you run the risk of giving your calf any and every bad infection that permeates the dairies including mycoplasma, salmonella, staph, kelbsiella etc one of the reasons that milk gets dumped in mastitis and calves can get those infections - you also have no idea what medications might be in the milk and if someone is (illegally) using gentamicin in dairy cows your calf could test positive for it down the road as it has an 18 month withhold.
Get a good quality milk replacer made from milk - not soy - with at least 20% fat 20% protein - feed the calf one bottle 4 x per day or 2 bottles 2 x per day spaced relatively evenly throughout the day - also make some sort of pelleted feed available as well as grass hay. If you have pasture that is also good and make sure you have a good mineral - I like crystalyx brigade tubs
If you have a herd the calf will learn to steal - if you don't have a herd and are willing to spend the time and money you can get decent growth - many bottle babies simply don't get enough to eat
I have an orphan right now - was 21 days early - his mother had cancer - he has learned to steal and is competitive size wise with his peers - I'll try to get a picture - good luck