Perhaps your vet might know a local Macaw breeder who can help you. Hand feeding can be challenging, but, hand feeding a large Mac .. is more than challenging from everything I have read. The large Macs are aggressive eaters, and because of this, can aspirate very easily.
Did the breeder know you have no hand feeding experience?
Did you choose to purchase an unweaned bird?
I'm just stunned a breeder would not only ship a bird in this heat .. that's bad, but ship an unweaned bird, at only 4 wk. old, to an inexperienced person?? That's just horrible!! At least he's got to be using Continental Airlines, they have temp. control holding areas for shipping live cargo, Delta doesn't, but won't ship at above or below certain temps.
Here's what I know .. but I've never hand fed a large Mac, I'm not a breeder, I just called a friend who breeds large Macs and got a quickie overview:
At 4 wks. hand feeding should be around 4 - 5 time a day .. each bird is unique, you just have to watch the crop and see how fast it's emptying.
Amount to feed can be anywhere from 60 cc to 110 cc per feeding average, again, this depends on the bird.
Don't forget .. formula temp. is EXTREMELY important!! 104 - 108 degrees is usually where breeders like to be. USE A THERMOMETER - DO NOT GUESS!!
Get the water hot first .. distilled water is preferred I believe .. then mix in the formula. Don't mix cold water and formula together .. then heat. If you're in a time crunch, most "box" pet stores <PetCo, PetSmart> sell the Kaytee Exact Hand Feeding Formula .. it's not the best, but in a pinch it's better than nothing. Your vet might be able to provide you with thy syringes, they're a little harder to come by in regular pet shops.
You'll need syringes .. Macs need larger syringes .. 60 cc is what was suggested at 4 wks, but you may want to get some smaller ones <35 cc> until you are comfortable handling a larger syringe.
Large Rubbermaid containers are great for using as a brooder .. I'd definitely invest in a thermometer to monitor the temp inside the brooder. Depending on how cool/warm you keep your house right now, you may need to supplement the heating source with a heating pad, or heat lamp <please, please, please, be careful using either of these, they can overheat the bird if not monitored .. THERMOMETER!!>
This whole situation has me puzzled to be honest. I know breeders will sell unweaned babies .. but usually they want some kind of reference that the person has experience in it. I don't know any breeders who would sell an unweaned baby to an inexperienced person, that just floors me. Did you tell the breeder you didn't know how to hand feed? Hand feeding large Macaws isn't for a novice from everything I understand.
Hopefully your Avian vet will be able to give a lot of help, or can refer you to a local Macaw breeder that might be willing to lend a hand.
Good luck, keep us updated!!