I’ve never seen the type of spring for a Howa magazine but Brownell’s sell spring wire for fabricating/bending your own magazine spring. Brownell’s also sell mag springs for various rifle magazine. I’d probably buy a spare Howa magazine then measure the spring.
Since the Howa is basically the same size gun as a Remington 799 or Zastava bolt action you might be able to get a mag spring for one of their mags.
Another option might to be to contact Weatherby. The Weatherby Vanguard is basically a Howa. Weatherby might be able to advise the manufacturer of the magazines or springs for the Vanguard.
Like someone else mentioned Wolff gun springs might be able to fabricate a spring or could be the supplier for the original Howa magazine spring.
Since the Howa is basically the same size gun as a Remington 799 or Zastava bolt action you might be able to get a mag spring for one of their mags.
Another option might to be to contact Weatherby. The Weatherby Vanguard is basically a Howa. Weatherby might be able to advise the manufacturer of the magazines or springs for the Vanguard.
Like someone else mentioned Wolff gun springs might be able to fabricate a spring or could be the supplier for the original Howa magazine spring.