Why go to Japan?  305 is made all over the world.  In fact you can get 305 with either 11% or 11.7% min Ni.
You can also get 304 with either 9.0% or 9.5% min Ni for the same the same purpose.
Do you need the strength, non-mag, or both?  Another option would be 21-6-9.
Have you spoken with Allegheny Ludlum?

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Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm

Ed
This is a continuation of my education into Stainless for low magnetic permeability.

Takasago was the first supplier I found that advertised a product that was tailored for deep draw with a guaranteed magnet spec. of permeability of 1.01 max. after draw.

Other suppiers only give typical - not max. and don't seem sensitive to the non-magnetic requirement.

I can spec. non standard ranges for the chemistry but I think the melt process, levels of impurities, rolling and anneal methods and other factors besides the chemistry also affect the stability and magnetic performance when stressed.

Ron

A-L, and others, melt different levels of Ni in 304 and 305 regularly.  The A-L Blue Sheet has perm vs cold work data.

The reason that no one will guarantee the perm after forming is that it depends on your tooling.  Tooling with higher levels of redundent work or surface working may show a little magnetism, even though the overall reduction isn't too high.

21-6-9 is even used for spring wire that must be non-mag.  You could try that.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm

305 is useful when you need excellent formability and no strain-induced martensite. If you only need the lack of magnetic permeability, then 316 will work as well, or 204 will be cheapest grade with very high austenite stability. Talk to Allegheny Ludlum. They make all the candidate grades. Your requirements aren't that difficult to meet.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

We just received the first parts off the deep draw tools.  Material was 316.  Chemical analysis indicates 16.45% Cr and 10.18% Ni.  The permeability varies over each part from 1.005 to 1.135 with the higher values nearer to the cutoff.  Just as a matter of reference, the 1.135 areas are barely attractive to a strong handheld magnet.
With our max. limit of 1.05, these parts are rejected.
We are getting these parts annealed but we really want to avoid this.
Our fabricator is attemping to locate some High Ni 305 for a sample run.

Ron

Ulbrich used to carry a 12.0% minimum nickel 305. You will get a fully saisfactory lack of magnetism with 21-6-9, as EdStainless suggested. Also 309, 310 will do the job very well. All of these are expensive because it is the alloy content which stabilizes the austenite.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/