1.  IBM
2.  Inland (General Motors)
3.  National Postal Meter
4.  Quality Hardware
5.  Rockola Jukebox
6.  Saginaw
7.  S'G' (Irwin-Peterson contract)
8.  Standard Products
9.  Underwood Typewriter
10.  Winchester
There are also some variations on these ten.  Irwin-Peterson made a couple hundred that never passed inspection and were never issued so the army gave the contract to Saginaw.  Saginaw management built them successfully in the plant formerly operated by I-P to the I-P design.  These are marked S'G'. 
A friend owns the rarest possible variation.  Quality Hardware subcontracted to Union Switch and Signal for some of their receivers.  These are marked UN-QUALITY.