Check out racksolutions.com, they may have what you need and their products are made in USA.
Hello everyone - I searched and the 2U Cable management arm (Dell Part 770-BBIP) is avaliable but it is not clear to me that  the 2U Ready Rails (Dell Part 770-BBIP) is compatible - it lists R7910 but not the tower 7910. Dell has a nice video showing installation but does not call out the part number in it!
Which ReadyRails for T7910 conversion to rack mount?