Comment 9 for bug 1009103

I guess your problem now is not within lxkeymap itself but in missing Paraguay xkb symbols file.
wander weather this could be the case when no one has actually created one?
If paraguay layout is similar to argentinian you could try to copy it and possibly amend it to your needs.

sudo cp /usr/share/X11/xkb/symbols/ara /usr/share/X11/xkb/symbols/py

You may want to add it to all list files /usr/share/X11/xkb/rules/ as well.

If you need more info please have a look at:
http://www.x.org/wiki/XKB
http://hektor.umcs.lublin.pl/~mikosmul/computing/articles/custom-keyboard-layouts-xkb.html

And if you decide to contribute your symbols file to X and Ubuntu then look at:
http://www.freedesktop.org/wiki/Software/XKeyboardConfig/Rules