If your Chimchar in OR/AS already has Iron Fist, then breed it with Ditto. When breeding with Ditto, the gender doesn't matter and the HA can be passed down anyway. Put your Iron Fist Chimchar in the Day Care with a Ditto, come back later, get the egg, and hatch it. The newborn Chimchar will have Iron Fist.
However, if your Chimchar in OR/AS has the Blaze ability, there is no possible way to breed Iron Fist onto another Chimchar without a female HA Chimchar. There are several different ways you can obtain Iron Fist Chimchar/Monferno/Infernape:
This is probably your best way to get an HA Chimchar. Make sure you offer something good in return, as HA Chimchar are very rare.
This method is hardly reliable, as the chances of getting the Pokémon you want are slim. Still, you might get lucky.
It is strongly unadvised to hack your Pokémon game, as it usually has nasty side affects. However, if you use a sight such as PokéGen to create a *legal* HA Chimchar (this means that everything will have to be done EXACTLY the same as a Chimchar obtained in-game) and transfer it to your game, hopefully everything will go smoothly. Only use this method as a last resort, if you ever do.
Use the Chat room on this site to see if anyone has an HA Chimchar that they're willing to trade or are able to breed one for you.. This is an effective way of getting Pokémon, but still inferior to the GTS. I have used it to obtain a Bagon that I was having trouble finding. Definitely try this out.
I hope that one of these methods help you to get the Chimchar you're looking for. Good luck!