Nystatin does come in a powder for oral use. I use it all the time. There is also a powder product meant for topical use, that is why the pharmacies are getting confused.
There are two companies that I know of that produce the powder for oral use:
Hi-Tech Pharmacal Co, Inc. Amityville, NY 11701 and
Paddock Laboratories, Inc. Minneapolis, MN 55427
Give the pharmacies the manufacturer information; many references organize the drugs by manufacturer, so it will make a huge difference in locating the info. If they still can't find it, I would question their intelligence and go to a better pharmacy.
Warning: nystatin tastes like dirt. It may make you consider death by candida as preferable. The good news is that your taste buds do adjust. While there will not be a day when you find you enjoy taking it, the experience will become less intense.
The info you have about stepping up the nystatin is correct. This will help prevent die-off problems- very important you keep a clear head with a baby around! Plus, I would strongly suggest that you supplement with molybdenum and pantethine complex.
My dosing schedule started with 1/16th teaspoon (once that day) and maxes at 1/4 teaspoon (4 times per day). It is stepped up to this does over 4 weeks, and then maintained at that level.
Your plan, the diet, nystatin and probiotics, is indeed sufficient. Also watch your newborn closely. My children were infected with candida through me, sadly I just didn't know the signs. In each child it appeared different, but here are some things to look for: excessive gas, colic, cradle cap, diaper rashes that don't make sense (diaper has been clean, but rash still occurs), difficulty sleeping, white stuff on tongue, mood problems (one helluva cranky baby), hypersensitive to touch/noise/stimuli.