depends...do you want to cheat for them? Otherwise you will have a though time trying to find 20 of them in shops.

hmm

Well, Im playing on the xbox360, dunno how to cheat on it? Unless you can tell me, Id rather cheat 20 daedra hearts instead of starting all over again. Appreciate it.

ah mate, i (stupidly) assumed you were on PC. I will se if i can dig up something.

EDIT

Check out this video..

It seems like you

a. begin to shoot
b. Double click on the arrows
c. THen drop the item you want to duplicate.

and wazzam

The "girl" (aragonian) that you have to talk to is just inside the foyar... so you don't have to be in the mages guild to talk to her.

Number 1 is a glitch I think.
Number 2; All I can suggest is travel back and forth between all vendors, and buy all the deadra hearts you can.