Well with all due respect to your body shop's experience, they aren't trying very hard. For professional consumer body shops, two paint manufacturers are very common: Sherwin Williams, and PPG. Both companies have a division that supplied paint to DoD of the CARC variety, so for certain they possess the color recipe. I sent an email to PPG yesterday "pretending I was in your situation", and they replied with a very helpful email today. Here are the cross-references they sent for the above three FS-595 colors:
Black (37030)- PPG brand code: 34184
Available in PRIME:
Concept- DCC
Delfleet Essential-ESSS
Delfleet Evolution-FDGH
Global-BC
Omni- MAE, MBC, MTK, MBX, MTX
Shopline- JB, JBX, JTX
Available as a color match:
Deltron-DBC
Green (34094)-PPG brand code: 403108
Available in PRIME:
Delfleet Essential-ESSS
Delfleet Evolution-FDGH
Available as a color match:
Deltron-DBC
Delfleet Evolution-FBC
Brown (30051)-PPG brand code: 25368
Available in PRIME:
Delfleet Evolution-FDGH
Omni-MAE, MBC, MTK, MBX, MTX
Shopline-JB,JBX, JTX
Color match available in:
Deltron-DBC
The email came with the same advice I would have given you (my slight edit in yellow): "If your paint supplier is having trouble making a color match to FS-595 colors, please have them call [the color lab for the manufacturer]. The color lab is a free service offered to licensed resellers, and we can match any color or provide the appropriate formulations for standard library colors from more than 50 color libraries including FS-595 color codes."
My last advice for you is that if you are having the body shop get the paint and they stonewall you, offer to do the research and talk to the paint vendor on his/her behalf. The body shop may just be afraid that if they make a mistake, they'll be on the hook for it, thus some reluctance.