Thank you for your post.
A button can perform an action or a script. Create a script that goes into Find Mode and puts the cursor in a Number field, and the numeric keypad will appear. The script could read something like:
Enter Find Mode 
Go to Field [ <your number field> ]
Pause/Resume Script [ indefinitely ]
Perform Find 
If you want to get a little more complex, you could switch to another Layout where only the Number field exists, enter the search criteria and then switch back to the original layout to see the results.
Let me know if you need additional clarification.