I think you can substitute a mixture of baking soda and cream of tartar, but I'm afraid I don't know the proper ratio.....
In this thread, they discuss leaving it out all together, one poster said you'll never missit:
http://cakecentral.com/cake-decorating-ftopic-618235-0.html
HTH
I think you'd miss it. I'd think the cookies would be extremely dense without the leavening agent. You can make paking powder... just take 1 tsp baking soda and add 2 tsp cream of tartar. If you aren't going to use it all right away, add 1 tsp of corn starch to absorb any moisture. 
You guys, you will not believe this...I'm sitting writting this so I don't throw myself down and CRY! I got last minute orders today for 40 cookies, I made two trips to store, mixed up my dough, and rolling it out seeing specks in it. WTF!!! This was a huge bag of flour I bought at Sams. AAAUUGG NOW, I have to wash everything, change clothes again, buy flour and start over. And these all have to bake, ice, dry, detail.....by 8am tomorrow!! PRAY FOR ME! AND on top of all that, I always try my dough before rolling it, and I've eaten these mysterious specks! They are black and reddish. PRAY for me even harder!
I did a search for you. The authorities seem to feel it is mold or flour beetles.
http://web.aces.uiuc.edu/vista/pdf_pubs/119.PDF
If it's a new bag,take it back!
And if you are allergic, take your medicine!
Thanks, 7yyrt! I was freaked out! I bleached everything down, and even threw away the huge bag of sugar I had sitting under it. I love a long way away from Sams, and I'm not gonna keep it around! BUT, I certainly will really check my flour really well from now on. Now off to check out that link. My SIL couldn't believe I've been on this earth this long and never encountered that before!
Shiney - what do you store your dry goods in? They are more likely to get buggy if kept in their original bags/boxes.
I normally buy the huge sugar and flour at sams, measure it up in double batch portions into ziplock bags and into the freezer. This time I didn't get around to it, and figured, well, it sits out in the store, so I'll get to it when I get time...and I never got around to it until I needed it. the flour I buy from the grocery store to use for my family, I keep in the fridge.
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