Could Find or Found?

"Find" is an infinitive form of verb meaning "to discover by searching, to obtain". Note that after do you should use the bare form of the verb: find, not found. ... The verb do carries the Past Tense, being transformed into did, so there's no need for find to carry the Past Tense too.

Could not find or found Which is correct?

'I could not find it' is correct because the bare infinitive 'find' is used after the modal verb 'could'.

Can found or could found?

So, you indeed should have used "could find". The modal verb, can is already in its paste-form: could. So you don't need to change also find.