Your ped was probably referring to baby rice cereal, and yes it's full of crap IMO!! lol It is very commonly said that babies MUST have cereal right at 6mos because their bodies run out of iron stores. I took an infant nutrition class and learned that it's not like they have a timer, and as soon as they hit 6mos BAM, no more iron! Between 6-12mos the iron stores do start to deplete and it is during that time you'll be working towards incorporating a variety of new foods into your LOs diet, many of which will include iron. Also, BM and formula do contain iron still, and they should still be the main component of your baby's diet until 12mos.
I did start baby rice, and DS never liked it, so at 7mos I stopped giving it completely and focused more on BM and finding iron rich foods to give him.
Depending on who you talk to as well, I have heard that grains in general should be avoided until almost a year because they are difficult to digest. Rice cereal can be very constipating.
I have seen available where I am organic baby cereals, so they are available depending on where you live. But TBH I wouldn't bother with those either. I won't bother with cereals at all with my next LO, in my experience it was a waste of time!!
BUT, with that said your doctor's advice is always important. My advice though is don't be afraid to do some research yourself as well and get lots of second opinions.