For Attack, go to B1F of Mt. Moon (this part). The only Pokemon you find there is Paras, which gives 1 Attack EV.
Those Pokemon won't give the most experience since they're low leveled, but their high encounter rates are very helpful plus they're easy to defeat. I always use them when EV training in FRLG.
The best way to keep track of your EVs is to write them down as you get them IMO.