What models do theses cases fit?

The cases have been test with the Volca Bass and FM instruments. As the cases for these are identical (thank you Korg! ;) ), the assumption is that they 'should' fit the other models without issue.
This answer will be updated once there is more feedback available.

Can you supply connectors?

The aim is to be able to supply complete kits with all you need. Although not all instruments can make use of six mini-jack sockets!This will happen once those components can be reliably sourced at a reasonable price.Currently, we are supplying the DIN socket for the MIDI output with the cases, along with 12cm of connection wires.

For you to buy your own mini-jack sockets, they are 6mm diameter. Details can be seen on the connector recommendations page

I already have a 3D printer. Can I download the design/s to print my own?

Investigations are ongoing to find a suitable platform for selling the models.
Obviously we can't just give away our hard work as we still need to pay bills/buy food/etc.
Once this is available, we would recommend making a test print first, as different printers may be calibrated differently.
As we have discovered from our own range of printers, although the case design may be accurate to the original, that doesn't mean it will emerge from each printer exactly to that size.

How accurate are the models?

About 90% accurate to the original injection-molded items. The designs have been amended to make them more suitable for 3D printing.
The battery tray, battery cover and (internally) the speaker holder all just slot in and use the original screws.

I've installed my instrument into the case and now it's really quiet?

Please move the rubber feet from the original case to the new one. If the speaker doesn't have any space between itself and the surface your instrument is sitting on, it won't be able to project any sound.