Hi Sandy,
First off I wanted to say thanks for all the work you've put into this as well as the awesome instructable! I've built my first version of the polargraph and it is working! I thought I'd share my parts list for any other folks from the US out there who might be interested.

I tried to buy all of the electronics pieces from adafruit to avoid a bunch of extra shipping costs from buying components from lots of different suppliers. It seems the only potential issue is that the stepper motors only offers 200 steps per revolution, but my drawings seem to have come out looking pretty good so far.

http://www.adafruit.com
Arduino Uno $29.95
Adafruit Motor/Stepper/Servo Shield for Arduino kit $19.50
(2) Stepper motor - 200 steps/rev, 12V 350mA $28.00
(2) Terminal block - 4 pin Euro-Style $5.00
9 VDC 1000mA regulated switching power adapter $6.95
2.1mm female/male barrel jack extension cable $6.00
(Note, that I didn't include the pen lift servo in my build)

http://blindsusainc.com/blindsusa-cord.htm#cord
20' of #10 Plastic Beadeed Chain (White) Item# CHN-97W  $18.80 + $5.60 s/h

http://www.shapeways.com/model/330572/2x_wide_polargraph_sprockets_5mm_axle.html
2x wide polargraph sprockets 5mm axle $8.62 + s/h
I had to file these a little bit to get them to fit on the stepper motor axle. Given that the Adafruit steppers have a notch on the axle it would be cool to make an updated version that would fit these, but the steps per rev are a bit lower so maybe that is a downside?

Extraneous hardware (I bought this at my local Lowes): 
Wire for motors - I found some alarm wire which was basically 4 wires bundled together. Perfect for the motors and the colors even nearly matched up. Cost: $0.17/ft

My gondola is currently pretty ghetto in comparison to the slick laser cut ones. Basically I cut a piece of PVC, drilled some holes through it and threaded some screws to hold the pen in place. Then I hot glued that to clear plastic 'cd' on the top of a spindle of CDRs that I had lying around. I bent some wire around the PVC pipe to attach the cord and the weights hanging off the bottom. All super low cost just to make sure it would work, which it does!
I attached the motors to a couple small pieces of wood using double sided sticky padded tape.
I'm drawing on a piece of hardboard which is thin, but cheap and also very smooth (on one side).

Now that I've got a couple test draws under my belt with regular printer paper and a fine tipped sharpie, I'm looking forward to testing out different pen and paper combos and bigger drawings!

Sorry for the crappy photo, but it's the best I've got for the moment.

Thanks again!
Jud

We are also building one in the US. I got my bead cord here in a loop (much much cheaper than by the foot). Got 14 ft for $20, then the shipping was like $6 to $8. But was better than continuing our fruitless search elsewhere. http://www.fixmyblinds.com

We are attempting the gondola with a piece of 5/8' copper. But obviously the size discrepancy with the 17mm ID bearings must be dealt with, haha.