In a magazine I read today, the article was written in present tense, about his/her experience overseas, in India.

I am confused about the use of the modals here. Can someone please explain to me their use?

I can walk to a market to find the electronics I'm looking for. The man I spoke to was right. And among the shops, I should be able to find a laptop.

1) If it is present tense, why would you bother saying you can or can't do something. Why wouldn't you just say you did or didn't do it, thereby showing if you can or can't: "I walk to a market."

2) What is the difference in meaning between "I should be able to find"& "I will be able find"?

1-- As it stands, your passage is a mishmash of tenses. I hope more text will clear it up.
2-- 'Should' is likelihood; 'will' is certainty.
So 'should' here is present tense and present time, and finding the laptop is something that is most likely about to happen?
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Yes. that is exactly how I understand it... with the caveat that you said this was 'narrative present'.
Is it common to have a present tense modal verb that states something you are about to do, rather than something you are doing at the time it was written?

For example, in sentence a, the tense explains actions that are currently happening in the present:

a) I walk home, and see my mother making dinner. I speak to her.

But in sentence b, the tense explains actions that are about to happen (I assume it is still called present tense, however):

b) I walk home, and should find the patient.
As I said, your particular excerpt is not clear without considerably more text, but yes, your sentence b seems possible to me.
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Mister Micawberyour sentence b seems possible to me.


Is should find in this sentence a past form modal tense referring to the present or future?

I walk home, and should find the patient.
I don't think it is useful to think of 'should' as a past form-- should/could/would have so many other uses. Here, for instance, 'should' certainly isn't the past of 'shall'-- it means 'ought to'.