Hello Bernt Damm and others,  While I don't have experience with the
Otto Accordion itself, I have restored a few piano accordions from the
1950s and 1960s, so this may be of some help.

The wax that holds the reed block in place is a mixture of beeswax and
rosin, and possibly other materials.  I know that the rosin is added
to the beeswax because it raises the melting temperature of the wax so
that reeds won't start falling off when you play your accordion outside
on a hot day!

The typical piano accordion has aluminum reed blocks with steel reeds,
one reed on the inside and one on the outside, tuned to the same pitch,
for the motion of the bellows in opposite directions when playing.
I suspect the Otto accordion uses only one of these reeds, unless the
accordion bellows is movable.  There is a leather flap that covers the
reed slot for the reed that is not playing at the particular moment.

When reattaching reed blocks, I heat the beeswax and rosin mixture in
a double pot, similar to a pot used for hide glue.  Do not get the wax
so hot that it scorches or it will lose its adhering properties.  Reed
wax typically comes with instructions for its use.  Be careful when
handling the reed blocks so that you do not touch the actual reeds.
Hold them on the edges like you would a coin, as this prevents moisture
from getting on the reeds.  Be careful as well to not drop any wax onto
the reed itself.

Because there are only narrow gaps between the reed blocks, a reed
"spoon" can be used to flow the new wax between the reeds, and
I usually follow this up with a pencil soldering iron set on low
temperature, to make sure the wax is firmly attached to the wood below.
I modified a soldering iron tip by sanding it flat on both sides and
thereby making it no more than 1/16" thick for this purpose.

If you need to replace the leather flap, be sure to use vegetable
tanned leather, and re-attach the flap using burnt shellac.  Some more
modern accordions use a different material than leather, and I'm not
sure what they would be attached with.

Here in the USA, I typically purchase supplies from the "House of Musical
Traditions" and here is a link to their accordion supplies page:

  http://www.hmtrad.com/catalog/winds/sbx/sbx-part.html 

They have the needed tools as well as the wax, leather flaps and so
forth.  I'm sure there are other suppliers, probably even more so in
Australia.  I hope this helps.

John Bartlett
Woodruff, South Carolina, USA