You can't get a Magmar directly without a Magby. Were it something like Snorlax, then you'd get only Snorlax but not Munchlax (without the Incense). However, though Magby is a baby Pokemon, you'll have to level it up.
I have one question though: why would you level up EVERY Magby to Magmar to use it again for breeding? Leave the Magby as a Breedject if it's not up to the mark in competitive IVs and Nature. You can re-use the same Magmar for breeding again and again.
In case you're doing it for the IVs, using a Power Object and Destiny Knot is a far more efficient method.