Can you only use short blanks, or any 22 rimfire short?
Natchezs has Fiocchi 22lr blanks; 100rds for $8.61
I've never tried any of their blanks, but all the Fiocchi ammo I've used has been excellent.
The link should get you to the Fiocchi 22 blanks:
http://www.natchezss.com/brand.cfm?contentID=productDetail&brand=XN&category=0&prodID=XN22LRBL
Fiocchi's site, but they don't say much about their 22 blanks specifically:
http://www.fiocchiusa.com/cat_blank.html