i agree with dc runics being best chance.
100% elemental is quite rare in any case, but remember you can enhance the metal and change some of the physical elemental property to an elemental one.
Material Bonuses
enhance bronze and turn 40 phys into fire
enhance agapite and turn 30 phys into cold
enhance verite and turn 40 phys into poison
etc
look for a 40/60, or 30/70 type weapon, and you should be able to enhance it for what you want. enhancing like this does NOT take up a mod slot - i tested with shadow and turned a 80% cold, 20% phys daisho into 100% cold.
that said, ive found the minos in miasmas dungeon to drop a lot of elemental weaps, and they have very little intensity or mods. read: less chance of something useless like spell channeling, mage weapon, luck, resist, or some other dumb mod being on them...
and remember you may have to go to expansion pack lands to get something specific. ie if i want a daisho, i have to go to tokono or anything released with tokono to find it. miasma seems to be a mondains legacy expansion if memory serves me correct, thats why you find elf, and not the japanese stuff there