where the hell can i fight marlboros

No, just the island closest to it.... :D

Sorry, just noting the irony of how you phrased your question. You fight them on the Island Closest to Hell. It's sort of in the south-western part of the map. IIRC Malboros also appear on the Island Closest to Heaven, which is in the north-eastern part of the map.

I think you can also find them in the Esthar region, particularly when you travel to the Sorceress Memorial and the other place than I can't recall.

the absolute best place to find them is the island closet to heaven (little tiny island in the north eastern part of the world) thats all i ever run into, malboro's and chimera's

I never encountred them on the isle closest to heaven, but to hell I can truly have cool slay the malboro feast XD o_O
At Eshtar they walk around as well, but only appear 'that' frequent that you may have fallen asleep when you finally battle one ;)
Be prepared! Know recover and Treatment ^_^ Junction status defense stuff to one person so he/she can restore the rest.

really thanks a lot
now i can finally go get doomtrain