The only available letters for mana codes are the following:  D, F, J, N, V

The Mana Code List:
A - Artifact
B - Black
C - Chaos
E - Brown
G - Green
H - Phyrexian
I - Infinity
K - Pink
L - Yellow
M - Colored
O - Orange
P - Purple
Q - Untap
R - Red
S - Snow
T - Tap
U - Blue
W - White
X - X Variable
Y - Y Variable
Z - Z Variable

Codes Used in Official Templates:   BCGIQRSTUWXYZ