And if you are not certain of the *exact* manufacturer, you can always just put in the country of origin and then indicate that it has no import stamp. Something like this for a Type 56 built at one of the unknown factories:
"China / No Import Stamp"
If you make a good faith effort at entering all the required bound book info specified in 27 CFR §478.125(f)
, you should have no issues should the ATF come a knockin' for an audit.