Fire spray usually works well, since you can move while casting. (But this won't work when they're already in your face.)
Melee attack also worked well for me. When I was going through 3-2 I had a fairly decent Moon Short Sword and could take them down with 3-4 hits. My aim was to kill them with successive hits, not allowing them to swing their swords.
Make sure and learn where each one is though - don't walk past any and you'll be able to take them on one at a time. Don't let them gang up on you.
You could also try using a shield with a higher Guard Break Reduction value, since this will reduce the amount of stamina used to block attacks. Buckler+4 has a GBR of 51. If you have a Leather Shield (54), Kite Shield (55), Knight's Shield (57) or even the Purple Flame Shield (60) you might have more luck blocking their attacks.
Pairing a shield with some kind of spear may also be useful, because you can attack without lowering your shield.
EDIT: After playing through a section of 3-2 using just a Leather Shield and a Short Sword (both base level), I have more hints:
Manage your stamina (the green bar on the top-left of screen). After blocking one strike, you should be able to hit a few times before running out of stamina. When this happens, back away from the Gargoyle and lower your shield, allowing your stamina to replenish. Then go back in with your shield raised and repeat.
Don't allow the Gargoyle to hit you while you have anything less than full stamina - shields are not effective if you don't have enough stamina to absorb the hit.
If you don't have enough stamina to absorb even one hit, you need to level up your Endurance and/or use a better shield.