Copying magento reviews one store to another is relatively simple by inserting new records directly in the database.
If you look at the table review_store you’ll see entries like:
review_id store_id 10 1
To copy the review to a new store you just need to insert a new record, for example to copy the review to the store with id 2:
INSERT INTO review_store VALUES ('10','2'); review_id store_id 10 2