Hi Rebekah!
I use those myself, and if my supplier does'nt have them in stock, they also offer an equivalent "OKI Bering" brand of similar lense quality. Another brand named "Omni View by Gentex are decent as are the brand named "Weldmark" and of course their website is:
http://www.weldmark.com Remember to type in the part number when searching for the lens so for shade ten, the P/n is: WM812410, WM812411 for shade 11 and WM812412 for shade 12.
All of the above mentioned lenses are of excellent quality IMHO as I too use them daily when depositing precise size GTAW welds on a consistent basis FWIW.
I usually have at least five of each shade I use which are 10, 11 and 12 so I'll always have more than enough on hand and I always order the clear lenses by the box and reorder when I get down to the last 12.
Respectfully,
SSBN727
Run Silent... Run Deep!!!