Did a quick google search and found this thread - maybe start with Remmeles and Production Tool as listed here.
Who has large VTL's - Practical Machinist - Largest Manufacturing Technology Forum on the Web
Searched "Who has large VTLs in US?"
Looks like Production Tool in Chicago is now under Monarch Companies:
http://www.monarchcorp.com/capabilities.html#heavy_fabrication
Remmeles is in MN:
http://www.remmele.com/AD/cap_index.html