Where can I find canti brake shoes for v-brake inserts?

Hi all,
I have a set of Shimano LX cantilevers of uncertain age. They have
replaceable cartridge pads, but unfortunately I'm told that the right
sized replacement pads are no longer made. Does anyone know where I
can buy cantilever brake shoes (smooth stem) that will take v-brake pad
inserts?

I'd like to be able to use the replaceable v-brake pads cause they tend
to be the cheapest for a given quality level, and it would hopefully
make replacing the pads easier. If anyone knows a source, please let
me know. Thanks!

Dan Lenski