I need 2 of 24 9 of BSI non-tilt single hung window channel balance.

Thanks for posting. See our S380-25 or S385-25 Channel Balance. The only difference between these two balances is the 'depth' of the bottom nylon shoe. See below. Measure your old balance's shoe depth to see what matches best.

Comparison of the S378, S380 and S385 balance shoes.

You then have to choose a stamp option, which reflects the strength of the balance. Your old balance's stamp is form an outmoded rating system. To know what stamp option to pick, weigh the window sash the balances support. You can use that weight to choose the right stamp.