Energizer sells single AA lithium batteries

http://www.energizer.com/products/lithium/default.aspx

Yes, and so do lots of other makers, but using these in place of 1.5V
AA cells will subject your unit to twice the voltage that it was
expecting. This is probably not a good idea.

No. Lots of other maker do not sell them. Just Energizer and they are
1.5 volts.

My point was that some devices and makers have attacked this problem
by making devices and batteries which can use either some number of
1.5V cells, or half as many 3V cells. They make special Lithium cells
which are shaped like 2 AAs side-by-side, so you get more than twice
the energy storage in the same space without going up in voltage at
all.

These double cased types have been around for a while. Energizer now
has single AA packaged lithium cells that are 1.5 volts