Feeding the parent birds a varied diet of seeds and/or pellets and fresh fruits and veggies would be fine You can get hand raising formula from pet stores. There are several different brands available depending on where you live
Mine are very partial to broccoli peas and corn which I buy frozen packs of, also a bit of wholemeal bread and any suitable unsprayed seeding weeds. Our birds have a seed based diet and with a good supply of veges etc from me their chicks are big and healthy. For handrearing mix I use passwells, vetafarm is also very good. Good luck with your babies!
My breeders usually like small white beans, corn, peas, dark leafy greens, along with seeds and sprouts. They will eat other things too, but they really love their beans and greens when feeding babies. Just offer lots of variety.
I can't recommend a formula. I have tried Kaytee exact. I like how easy it mixes, but I don't feel like it ever puts enough weight on my chicks, especially compared to when the parents feed them. I have tried a couple others but didn't use them long enough to really judge them. I just remember they didn't mix as smoothly and easily. I have since only started handfeeding in emergencies, so I'm certainly not the person to give advice of formula. Kaytee is most commonly available around here, but I'm about positive there is something better.
I see that you're from NZ (stalked your profile, sorry xD) so I would recommend either Passwells or Vetafarm. I personally like Vetafarm, it did wonders for putting weight on my stunted chick, and it mixes beautifully and it smells good (I tried a different, not so well known brand and it smelled terrible). I haven't tried Passwells but I have heard good things about it.
I would highly suggest starting them on sprouts, they are really beneficial and worth having as part of their diet (you can read more about it here). We feed ours sprouts, and our babies are always more than happy to dive into them from the time they start weaning.