ISO Code or 3rd party app for drop down menu

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Hello! I am wondering if there is a code or a third party app that can be used to integrate a feature on my website that will give an option for a double drop down menu for products. For example, all my products are in square/rectangle shapes (artist canvas). There are thousands of custom sizes and with different options. 18" x 24" OR 36" x 36" - so to dropdown to each of those numbers (from 4"-144" on each side) Thank you