This same question was just asked in the last week or so. There are no known kits with 0.9mm mechanisms. Only thing you can do is buy a Pentel at Wal-Mart and use the internals to make your own.
Not to sound testy cause there are others who do testy, but this has been asked about every week for the last month.[]
"There are many types of pencils made by Pentell, so be sure you buy the <u>"SHARP"</u> model. They come in 0.5mm, 0.7mm, and 0.9mm. Any size will work."