I wonder if anyone know if it is possible (and where it is possible) to order a new horizontal stabilizer to at 10-300 Goldberg Ultimate plane ?

There is a parts listing, with part numbers and prices, at the bottom of this page:
http://www.carlgoldbergproducts.com/.../gbga1053.html
If you cannot order directly from them, a hobby shop should be able to order it for you.

It is pretty easy to build one. I could Zerox the blueprint and send it to you. It is built from 3/16"x1/2" balsa and sheeted If memory serves me.

David