Hey David,
this was asked here the other day, a truly U.S. American spindle manufacturer is cncdepot.com
and there is also Glockcnc.
However Germany and Italy are countries with strong machinery industry, so you find → a lot of spindle manufacturers there…
Possibly there are much more spindle manufacturers in the US but it is difficult to find them since they do not address hobbyists. Mechatron is a manufacturer that addresses consumers and hobbyists directly, that’s what makes it easy to get a spindle from them.
Note that there are also big differences between cheap chinese spindles and expensive chinese spindles. See here the impressing video of noise and vibration comparison test between a cheap no-brand chinese spindle and an expensive brand chinese spindle.
Tom @TMToronto in this forum uses a spindle from this chinese brand (search for “@TMToronto ATC build”)
Here is the DELIXI CDI-EM60 Series VFD manual.DELIXI CDI-EM61.