Just increase your plot grid:
fig = plt.figure(figsize=(10,8))
a1 = fig.add_subplot(521)
a2 = fig.add_subplot(522)
a3 = fig.add_subplot(523)
a4 = fig.add_subplot(524)
a5 = fig.add_subplot(525)
a6 = fig.add_subplot(526)
a7 = fig.add_subplot(527)
a8 = fig.add_subplot(528)
a9 = fig.add_subplot(529)
a10 = fig.add_subplot(5,2,10)
fig.add_subplot(52X)
is short hand for 5 rows, by 2 columns, Xth plot. Your code only allows for 9 plots because it was a 3 x 3 grid, (fig.add_subplot(33X)); increasing it to a 5 x 2 grid allows for a 10th plot.
You can rearrange the column or row count as you please to get whatever look you desire.