Spanish Dvorak Keyboard
If you hold a key down (like n) you should get a popup menu with accented versions (like ñ). Also the usual option deadkeys (option n, then n) should work.

An example of a custom layout someone has made for this is at

http://djelibeibi.unex.es/dvorak/

http://djelibeibi.unex.es/dvorak/ES%20Dvorak.keylayout

It is pretty easy to make your own with Ukelele:

http://scripts.sil.org/ukelele