As suggested on this forum, I bought some and am giving it a try...

http://www.dharmatrading.com

There offer several weights, 5, 8, 11, and heavier.  I bought some 5 and 8 and also a small sample of 11.

The 5 is the only way to go for wing covering.  The 8 might do for front end or dihedral reinforcement.  You could use the 11 for a tent.  Somebody explained units of measure, but I forgot the story, just get #5.

I also bought a little jar of bright blue dye.

I cut off enough to cover a plane and proceeded to wash off the sizing.  In the absence of instructions, I put the silk in a pail of hot water over night, then rinsed it in the morning.

The dying was simple.  Step One is wait until the wife is safely out of the house.

Boil some water in a tea kettle.  Put the boiling water and a few ounces of vinager in the pail, then sprinkle in some dye crysals, and stir. 

Then put in the silk and stir some more.  I added more boiling water, then dumped out the dye water and rinsed with tap water several times.

I hung it out to dry on some chairs, and to my surprize, the dye was perfectly uniform, first time ever!!!

Don't expect a beauty queen !!

It's been 100% humidity and drizzle throughout this process.  "Blushing", (humidity trapped in the dope) is the result. 

Randolph recommends "waiting until the humidity is under 50%" as a "cure".  I didn't have the time. The next race is Saturday.

All done !!!

Two and a half days from dying the silk to ready-to-fly. 
Five coats of Randolph CAB clear, 2 dope to 1 thinner, brushed on.  I could have done better if I let each coat dry for a day, but time flys and I want to fly, too.

Final weight is 26.6 ounces, a fractional savings for the previous off-brand plastic job.

The silk is of the 5.5 (lightest) weight.  I've seen the same product also listed simply as "5", same-same either way.

The first two on the menu,  5 mm "Silk Habotai" in either 36" or 45" width.

I went with 45" x 2 yards, as a test programe.

I bought 45" on the theory that a big piece of material might result in lower scrap losses.  However, the stuff come off a big roll, so you could buy 36" by a mile or 45" by a kilometer, whatever covers your plane.

http://www.dharmatrading.com/html/eng/1344-AA.shtml?lnav=dyes.html

That link should get you to the right dye.  I bought #623 Brilliant Blue - that's MY color, you pick something else!

The silk ( HS536) costs only $2.05 per yard in a quantity over 11 yards, thus, your 12 yards will cost you only about $25 (the cost of a one-yard pack from traditional sources).   On the other hand, you could pop about $34 for 12 yards of the 45" wide stuff (HS545), and really be "covered".

The dye is about $4 for a 1/2-ounce jar of crystals, which should last a lifetime.  Buying crystals vs liquid solves a shipping concern.

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The next cost hurdle on your big job is the dope & thinner,  Good Luck. 

I buy Randolph from airport supply shops.  If you do a search for "Randolph dope", you will get to their web site which will list about 20 dealers in the US of A, of which one is in Carmichaels, PA.