A tip for those of you who are interested.
In this case, 'konnte' is in the past form, Präteritum (one of two forms of past tense)
The way you conjugate it is following:
ich konnte du konntest er/sie(singular)/es/man konnte
wir konnten ihr konntet sie(plural)/Sie(formal) konnten
Notice how its not too different from the present tense conjugation. The 3rd Person Singular is the only one that is different when it comes to endings (its takes on the 1st Person Singular ending of -e).
The conjugation follows the same pattern with the other Modal Verbs (müssen, sollen, dürfen)
Ah and the Umlaut is dropped in all of the Präteritum cases of the Modal Verbs.
The emphasis is different in that sentence. It emphasises that "I could not find it [but I could find something else]".
But anyway, this sentence is translating the German into English. In the opposite direction, it might be accepted as a possible translation, but it's not the best one unless the English sentence is also worded to convey that emphasis.