El vendedor me ofreciã³ esos guantes cuando busquã© gafas de sol

El vendedor me ofreció esos guantes cuando busqué estas gafas de sol.

Explanation: The sentence can be translated to:

"the salesman offered me those gloves when i pick ___ sunglases"

Now, sunglases or "gafas de sol" is a feminine plural word, so in the blank space, we can put any pronoun that works for plural feminine, for example:

las (the), estas (this ones), esas/aquellas (those/that ones)

So we can choose any of those options to complete the sentence and the sentence will be correctly written.

For the context of the sentence, we know that the person talking "picked up" the sunglases, so he/she may have them, in that case the correct option will be "Estas gafas de sol" or "This sunglases"