I am grateful to A Bouazza for the information I could not have reached without his/her help.
I would like to quote from Jansy's mail personally sent to me:
The ending of "sericanette" might suggest a synthetic imitation of a product.  False Chinese silk, for example.  Lots of articles that imitate for example, embroidered linnen are called "linnette" or something similar ( in Brazil, "Linholene" ), grape soda becomes
 "grapette".  I suggest something artificial  or synthetic is announced there. 
That reminds me of "alabasterette" (imitation of aragonite--but why not "alabaster"?) of which the figurine of a female skier is made. Perhaps "sericanette" is mentioned there in order to make us remember that we read about the making of the figurine (of the other "-ette") many chapters ago.
----- Original Message -----
From: Donald B. Johnson
Sent: Monday, December 20, 2004 11:34 AM
Subject: Re: Fwd: TT-26 Introductory Notes

----- Forwarded message from mushtary@yahoo.com -----
    Date: Sun, 19 Dec 2004 11:42:47 +0100
    From: "A. Bouazza" <mushtary@yahoo.com>

===> 101.13: (sericanette): Seric, archaic, "Chinese." In a "Words" file Nabokov
kept, he marked off as used in TT "Sericana, region of SW China (in Milton)"
(Brian Boyd's note to the LoA edition).<<<

One would like to add that, as J. Bodenstein noted in his unpublished
dissertation "The Excitement of Verbal Adventure", with this neologism VN
wanted to denote "Chinese silk", since the eponymous region has been known for
its silk since Classical times.

A. Bouazza.