I wouldn't call these brifters unless the brake lever is integral to the shifter, these are trigger shifters. Have you tried cleaning them? How old is the bike? I have replaced some old ones with Shimano shifters sold by Niagara. The 6 speed shifters go for about $8, the 7 speed go for $12, complete with cables.
I have never had that good of luck rebuilding these shifters, probably a lack of skill on my part. So I tend to toss the old ones. Some report decent luck getting them working again. But for $12 complete with cables, hard to justify much work on old ones at least.
Neither of these below have integral brake levers:
7 speed:
http://www.niagaracycle.com/product_...ducts_id=15889
6 speed:
http://www.niagaracycle.com/product_...oducts_id=6144