Some time back I decided the spindle bearings on my X4 Speedmaster sounded bad. I couldn't get anywhere with COA or SA in getting a replacement spindle so I hunted around for a 220V one and a 110 to 220V inverter to replace the original inverter. It was an expensive solution , but it was about the same cost as an OEM Syil spindle which I did not seem to be able to get anyway. I bought the inverter (VFD) from Drives Warehouse and when I struggled to get it setup properly one of their guys called me back long after their local hours and helped walk me through the setup. This machine is still 110V in for everything, but because of the new setup it uses more readily available 220V spindles now.

The biggest problem and the highest drive of the cost was that my X4 Speedmaster was setup for a 62mm spindle instead of a more common 65mm spindle. I did have the advantage of knowing most of the basics of setting up a machine already.

My experience is not the same as yours, but I expect a third party spindle controller may be possible to get to work with your machine.

As a side note: We just had a conversation on the CamBam forums about old caps blowing up on inverters (and other equipment) after a long period of storage. There is supposed to be a procedure to reduce that likelihood if you do it before powering it up, but I don't think I could repeat I accurately.