Hey John... You can retain the current foundset by finding the "Order Number" in a new window.
So the script should be like as follows..
Enter Find Mode
Set Field 
Constraint Found Set
... // Do your work here
Please let us know if it fulfills your requirement :)
It's also possible, in some cases, to use Go to Related Records (without specifying that it match the current record) to make the specified record the current record within the found set.
You could also use a script to loop throught the found set to find the record and make it the current record.
Its possible if you can Go to related records for the current search set for the company to the company orders and from the related records you can get the found set for the Order number, performing a find on the related records for the order number.