Possible copyright/trademank issues. Whilst the original Harmony company shut up shop in 1975, there was a distributor, Westheimer Corp, who sold reissue Harmonies (including an H22), and since 2018 there is a new Harmony company that currently sells new design guitars, but looks to be ready to sell some reissue types as well. https://www.harmony.co/

So you'd have to search into the details of what is and what isn't currently protected.

It looks like the H22 was created by utilising the body from a Harmony Rocket (H53, H54 and H59 models) and fitting it with a short scale neck, which, by necessity of fitting the existing pocket, was thin all the way up. Which means that once you've made the body, you can also do a guitar neck for it and make a Rocket model as well.

But the secret to getting anything like a decent copy is sourcing some decent gold-foil pickups. The pointy rotary selector switch is also fairly unique and is likely to be hard to source.