What Can I Give My 3 Weeks Old Pups To Substitute The Mothers Milk?

My emergency formula is 2 parts similac (baby formula) 1 part water w/ 1/2 tsp sugar. Warmed to the touch. Place in a large shallow plate. Try this after they've been awake & mobile for awhile & not feeding off Mom. The hungrier they are the most likely they will eat. Add in some esbilac at next feeding & a little more each time, They'll get use to the taste in a day or 2, till there only eating esbilac. In a week or so they could be trying wet food at any rate. 

Cow's milk or human baby formulas are not appropriate for use in puppies and can lead to diarrhea.  It is best to use a puppy replacement formula.  There are other available commercial puppy milk replacers besides esbilac.  Other formula's are for emergency purposes only.  At 3 weeks puppies can be started on a puppy food mush to supplement nutrition and start the weaning process. 
Deciduous tooth eruption depends slightly on size and breed.  Typically incisors erupt at 3-4 weeks of age, canines 3-4 weeks of age, and premolars at 4-12 weeks of age.
If you have any concerns about the health or nutrition of these puppies have them examined by a veterinarian.  Puppies can fade away fast.

Call your local vet.  They can tell you what is safe to use and they have the right formula you can use there and buy from there.  Good luck.