Create a query of all your possible part numbers. This can be done pretty easily from the table holding all your data, i.e. something like
Code:
SELECT DISTINCT PartNumber
FROM MyTable
ORDER BY 1
You will obviously need to change the field and table names to match your database, but this will list each part you have exactly once and place it in alphabetical order.
Then, if you make your Part Number field on your Form a Combo Box, you can use the Query created above as the Control Source of this Combo Box. So then your users can just select the value in your Part Number field from a list instead of having to type it in.