I think the formula companies sponsor a lot of training for hcps where they imply that breastfed babies don't get the same amount of iron as babies who are out on follow on milk which has enough iron to knock an elephant over. That follow on stuff and the ridiculous TV ads drive me crazy. Just ask my husband!
Surely babies ingesting that much iron just poo it out. We can only absorb a certain amount of iron and we get rid of the rest.
By 6 months a baby can pretty much eat anything so even sucking on a piece of red meat and spitting out the meat itself will give enough iron. You can make things like spaghetti bolognaise, meatballs etc to encourage them to eat iron rich foods. Give them steamed broccoli florets to suck on. At 6 months they only need a small amount of food so think about quality over quantity.