I called Bongiovanni. They told me the piece in their catalog is the unfinished concerto in A major as kalliwoda said.
They do not have the orchestral parts of the concerto all'antica as mentioned in Musikproduktion Hoeflich website.
the solution seems to be:
1. buy the pocket score by Musikproduktion Hoeflich. You can by via paypal. Cost 29 euros http://www.musikmph.de/musical_scores/vorworte/780.html
Respighi, Ottorino Concerto all' Antica per violino ed Orchestra (composers autograph) 780 142 29.00
2. search in university libraries.
I found it at the university of washington. http://www.lib.washington.edu/Music/Acq ... Aug09.html
Author: Respighi, Ottorino, 1879-1936.
Title: Concerto all'antica : per violino ed orchestra
Pub. Info: Munchen : Musikproduktion Hoeflich, [2008?].
Location: Music Stacks
Call Number: M1012.R47 C6 2008.
try to write/call them. It can be they scan and send the pdf. Or ask someone in the USA to scan for you....
3. organize a concert and rent the parts from Ricordi.
it can be it is no so expensive. Have you asked for it?