To verify that work is available in print and can be purchased/rented, we recommend the following source:
Zinfonia: Music Publisher Portal *Note: This site requires you to login at first, but is free.*
Zinfonia links to individual publishers for information about rental/purchase of complete orchestral parts.
Luck's Music Library Includes information on for purchase and some rental parts.
You might also find these sites useful:
Theodore Front Distributor site for purchases from various publishers, especially European ones.
JW Pepper Private retailer for sheet music; one of the oldest and largest in the country.
SheetMusic Plus Distributor site for purchases.
WorldCat Collected library catalog for North America and Europe. Use this database to determine if a published work exists or not.