List/Record field not searchable

I 'assumed' this would work (You know what they say about assuming...) but it looks like it doesn't.

Here's the deal:  I have 1,600+ records (ICD9 codes - medical diagnosis).  When we enter a sales order, we need to include 1 or more of these codes for each product or service.

I've added a transaction column field (List/Record).  When editing a line item.... all I get is a simple drop down list which is completely unusable due to the amount of records.  I was hoping for something like the 'item' column where you can type the first few letters and it will pop a list of results.