Spingear produce koma under their own brand. They're available in a few places online, but the less expensive ones are only available from Spingear directly or via retail in Japan.
The premier koma series. Made of CNC delrin with a steel axle. Unlike traditional koma the tips are shaped to help capture the string. It's sold in a few places as just the 'koma'.
The V3 has an acorn shaped tip and normally ships with no weight rings but they can be bought and fitted separately. The V4 has a fine spike tip with a flat shelf above it to capture the string and is only available with an inner (Kodachi) or outer (Kabuto) weight ring.
There are also clear V3 variants made in polycarbonate instead of POM. At some point straight and shorter straight replacement axles were also available.
The V4 Kabuto can be fitted with the clear plastic cap from the Hibari. The V4 Kodachi has its own distinct cap.
Note that as this model doesn't have a flat top it's hard to throw with just a knot in the string. Tying a loop to put around the top of the axle works better.
Prototype model. Made of CNC delrin with a deeper body shape than the hayabusa and only available with a weight ring installed. Seems to have been discontinued.
Polycarbonate budget model. Same shape as the hayabusa. Straight axle. Comes in translucent colours.
Injected POM budget model. Same shape as the hayabusa. Straight axle. Comes in solid colours.