www.fashionfabricsclub.com.

Discount high quality fabric, searchable by color, fabric content, washability, etc. No joke - I've bought $15/yard fabric for $5; italian wool for $8/yard; etc. GREAT selection of decorator fabrics.

Samples are available for nominal cost.

I love that color combination. Here is one possibility.

http://www.calicocorners.com/product/designer+fabrics+for+the+home/shop+fabrics+by+color/yellow/vintage+blossom+citrine.do

Oops, part of the url seems to be cut off. Trying again.

http://www.calicocorners.com/product/designer+fabrics+for+the+home/shop+fabrics+by+color/yellow/vintage+blossom+citrine.do

That bathroom is the best. And that show is terrific. Don't we ll need a Tommy?

Here's the fabric:
http://www.kingdominteriors.co.uk/catalogue/Sanderson/fabrics/EtchingsandRoses/21282

But here are some other (lower priced)options:

I first thought this was a toile, so searched and came up with this -- I think the right colors.

http://www.onlinefabricstore.net/drapery-fabric/toile-drapery-fabric/waverly-country-life-vintage-lake-fabric-.htm

But then I found this floral -- I think it's less fusty, more modern than sarah's and could be awesome although difficult to find enough yardage.

http://allegrofabrics.com./item_1968/Robert-Kaufman-Free-to-Grow-Organic-Cotton-Yellow-Flowers-Summer-Fabric.htm

another modern twist on grey and yellow floral:
http://www.spoonflower.com/fabric/385799

this is a straight up yellow and white toilee-y floral -- you could add a grey grosgrain ribbon trim.
http://warehousefabricsinc.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=WFI&Product_Code=ODFLWYEW&Category_Code=outdoor-upholstery-fabric

pamh
howtorunyourlife.blogspot.com

Amy Butler has some really nice grey/yellow combinations...
http://www.amybutlerdesign.com/products/fabrics_top.php?fabric=nigella&flid=11

pamh, wow, that warehousefabric store looks amazing. THANK YOU!!!

This is slightly different, but I think pulls your colors together perfectly -- although, it isn't exactly a country vibe, it is really a great design:
http://www.westelm.com/products/butterfly-shower-curtain-b575/?pkey=cshower-curtains

I love the delicate illustrative design with great pops of color. Yes, not exactly what you asked for, but I think it would work very well. Enjoy!

From HGTV.ca

drapery fabric
Sanderson available through Telio
160 Pears Ave., ste. 400, Toronto, ON 1.877.254.9855
www.telio.com

drapery rings & brackets
Designer Fabrics
1360 Queen St. East, Toronto, ON
416.531.2810 www.designerfabrics.ca

drapery finials
Invu Drapery
1.866.572.2472
www.invudraperyco.com

custom drapery rods
Rene Petitjean
705.466.5895
www.renepetitjean.com

Already plenty of good answers, so I'm not going to feel bad about posting this unhelpful comment: Hey, I loved that bathroom too! I hate hate hate toile, but I loved those curtains. I just recently discovered this show and have set the dvr to finding all the old episodes being run in the middle of the night here. She is making me rethink many things I used to dislike.

Here's two more options:
http://www.fabricguru.com/cart/index.php?target=products&product_id=240941&page=1

http://www.fabricguru.com/cart/index.php?target=products&product_id=81955&page=1

Also this, which is grey, not yellow, but could certainly be trimmed out in yellow somehow. I just think it's really pretty:
http://www.fabricguru.com/cart/index.php?target=products&product_id=377872

Here's something similar and it comes in a lovely aqua colourway as well:

www.tonicliving.com

I am Canadian so have loved Sarah and Tommy for years. What is even better is everything on all of her different shows she has done, HGTV posts everything on line of where she bought it, sprayed it, built it, found it, etc., etc. Usually posted a day or so within being aired on HGTV.