Matt,
Sorry, yes, there are in Customer options. My memory is sometimes fading.
There is no need for the Find window to pop-up, just check Require _and_ Prompt for Customer selection in Customer Options and make sure that in Options | General | the Don't remember list sorts is checked. It will then always sort by the first column on any list. If this is a problem elsewhere, leave it unchecked and you _may_ have the click on the Account Number column header before scanning the card. This is assuming that the number on the card represents the Account Number, which it should.
Do you already have the cards printed? If not, make sure to have the Account Number bar code and/or the mag stripe scannable. A bar code will always work, a mag stripe may have to be specially designed and created or a second mag stripe reader will be required.
Mag stripes are usually formatted like a credit card is, you _do not_ want this!! You want a mag stripe to contain only the Account Number and an enter symbol. If you cannot get your card maker to do this, then you will need a second mag stripe reader at each register. Before you have hundreds printed and encoded, test an actual card first!!
My recommendation is to print your cards with the Account Number only as a bar code, not a mag stripe, and with the numbers also printed on the card. It will be easier and cheaper.