Lawrence Paterson's book on U-564 gives the amount and type of torpedoes they used in their patrol in the Western Atlantic in 1942. 15 G7e's and 2 G7a's. They got a couple of torpedoes from another u-boat, transferred them in the middle of the Atlantic. Only G7a's could be carried in the outside storages. Later during the war the outside storages weren't used anymore as it was suspected that carrying them had caused u-boats' sinkings in depth charge attacks, and the air patrols made it too dangerous to be surfaced for any length of time.
JFO! mod by Rudewarrior has all the known orders about torpedo loadouts given by BdU during the war. Unfortunately U-boat Archive's BdU KTB only has some orders about torpedoes, so not a lot is known about the loadouts. Hopefully someone has more complete knowledge on this.
Here's the ordered loadout for April 1944:
http://www.uboatarchive.net/BDU/BDUKTB30350.htm
Serial Order No. 40.
April 1944 issue.
Equipment with torpedoes.
1) Each type of boat is in future to be equipped with torpedoes as follows. All previous orders are cancelled:
a) Atlantic:
Type VIIC forward 3 TV, 2 FAT I, 3 T III FAT II (or 5 T IIIa FAT II)
aft 2 TV
Type VIIC forward 3 TV, 5 T IIIa LUT
(LUT boats) aft 2 TV
Type VIID forward 2 TV, 2 FAT I, 4 T III FAT II
aft 2 TV
Type IX B and C
North Atlantic
forward 3 TV, 3 FAT I, 4 T IIIa FAT II (or 7 T IIIa FAT II)
aft 2 TV, 2 T III FAT II
Type IXD forward 2 TV, 8 T III FAT II (or T IIIa FAT II)
aft 2 TV, 2 T III FAT II
upper deck 9 FAT I (or T I)
Type XB aft 2 TV, 5 T III (or FAT II)
b) Northern Waters:
Type VIIC forward 3 TV, 5 T III FAT II
aft 2 TV
c) Mediterranean:
Type VIIC forward 3 TV, 5 T IIIa FAT II
aft 2 TV
d) Black Sea:
Type II forward 1 TV, 4 T III