Allow only 1 or 2 pcs per specific product

Hello, I have a question,I can not solve myself... We sell cosmetics and we offer testers for certain products. We would like to offer those testers for free (customers would only pay shipping), but we would like to limite the amount of testers that can be ordered. The reason is, we don't want a customer to be able to order free 10 testers instead of buying one original size. But they should be able to order 1 or 2. allother producst would have no restrictions, so this should be able to set per specific product not in general.

I would like to solve it by module, no hard coding or changing the core files. We use OC 2.3.

I hope I was able to explain it well. Thank you for any suggestion.