Not sure how you would do it through Navicat or SQLYog as I don't use them. But using the standard mysql client you can do the following. Just replace the table names and search criteria with whatever you need.
Open up the mysql client and type:
Code:
CREATE TABLE custom_items LIKE items;
INSERT INTO custom_items SELECT * FROM items WHERE id BETWEEN(50000,60000);
Then export that table in whatever method you feel comfortable. Either through Navicat/SQLYog or by simply running the following from a command prompt/shell:
Code:
mysqldump -n -c -t -p <database_name> custom_items > custom_items.sql