Where can I purchase a replacement foot switch?

Make sure--Does the machine take a short shank presser foot? If so, you can replace it with a short shank zig-zag presser foot. You can probably go to a regular sewing machine repair shop and find a replacement presser foot.

**NOTE--the links below are examples of what is available. I cannot vouch for these vendors as I've never purchased from them. Do your own due diligence before purchasing!!!

Here's an open toe presser foot:
Open Toe embroidery satin stitch foot Low Short Shank Babylock Bro White...

or a regular zig-zag foot:
http://www.ebay.com/itm/Vintage-ZIGZAG-FOOT-Fits-Singer-Pffaff-Other-Mfrs-Low-Short-Shank-Apps-MPN-C24-/401237995786?hash=item5d6ba5f10a:g:8UcAAOSweWVXcubS

OR you can buy a short shank adapter and a kit of snap-on presser feet that will give you a big variety of different kinds of presser feet, probably including a zipper foot, hemmer foot, 1/4" quilting foot, darning foot, teflon foot, etc....(probably more than she will ever use!) The snap-on kits are available online, try eBay or some of the other sites. They most likely are not Singer brand, but are most likely generic. However, if your granddaughter is just learning, this may be the broadest variety of choices.

These are examples of snap-on presser feet available.

Snap-on Adapter example (most kits do not include the adapter):
http://www.ebay.com/itm/Low-Shank-Presser-Foot-Holder-Adapter-Snap-on-Singer-Kenmore-Juki-Elna-Janome-/222013366993?hash=item33b10722d1:g:Sa0AAOSwJb9WsRpp

Snap-on kits- examples:
42 PCS Domestic Sewing Machine Foot Feet Snap On For Brother Singer Set...

http://www.ebay.com/itm/1-Set-32-Pcs-Domestic-Sewing-Machine-Foot-Feet-Snap-On-For-Brother-Singer-Janome-/282017920492?hash=item41a993f5ec:g:MrAAAOSwMVFXH3rP

...

fortunately manufacturers take a long time to change walking feet so go to a janome sewing machine repair shop and they may have one that covers a range of years

128results for janome foot control

Amazon com janome foot pedal

Janome Newhome Parts by Model

I would suggest that you visit the Janome Australiasia website, and go to their Find a dealer page, link is http://www.janome.co.nz/janome_store_location1.php?sid=nz

There should be a Janome dealer near you and they should either have a foot or order it in for you.

Other option is to buy one from Ebay but I've always preferred to support a local dealership as you can benefit from their product knowledge too.

Here is link for the 1/4" foot
http://www.janome.co.nz/sewing_accessory_1.php?aid=200-318-000&gid=1/4 Inch Seam Foot

try www.sewingpartsonline.com for replacement parts

http://www.sewingpartsonline.com/presser-foot-shank-elna-janome-kenmore-804509000.aspx looks like it is the one you need I think.

try sewingpartsonline.com

try janome website for the walking & embroidery feet & manual
try these sites for manuals also
(pdf) manuals online.com
sewusa.com
sewingmanuals.com
mastersewusa.com
sewingmachineplus.com
homeappliance.manualsonline.com

High Shank Machines are all the Janome Embroidery models MC 8000, MC 9000, 10000, 10001, 11000, 200E, 300E, 350E....etc
If yours is not an embroidery machine, it has a LOW SHANK .....the higher shank allows for easier access for the embroidery hoop.

Try here:

http://stores.ebay.com/Glendive-Sew-N-Vac_Power-Cords-Foot-Controls_W0QQcolZ4QQdirZ1QQfsubZ16QQftidZ2QQtZkm

If you go to the Janome website of your home country they will have a dealer locator page where you can find your nearest dealer.
Explain the problem and they will be able to order the replacement part for you.
You may find that parts availability at this time of year will be restricted as many businesses and suppliers close for several weeks.