Breakdown of Я должен где-нибудь это купить.
это
this / it is
я
I
купить
to buy (perfective)
должен
must, have to (должен, должна, должны)
Questions & Answers about Я должен где-нибудь это купить.
Why use где-нибудь instead of где-то in this sentence?
The suffix -нибудь is used when you mean 'anywhere at all' or when the place isn't specific yet. Since the speaker hasn't bought the item yet and doesn't have a specific store in mind, где-нибудь is the natural choice. If they used где-то, it would refer to a specific place that the speaker just doesn't know or forgot.
Why does the speaker use должен instead of a regular verb for 'must'?
In Russian, obligation is usually expressed with должен, which is actually a short-form adjective rather than a verb. Because it acts like an adjective, it changes based on the gender of the subject. Here, the speaker is male (Я должен). If the speaker were female, she would say Я должна.
Could I put это after the verb, like купить это?
Yes, you absolutely can. Russian word order is very flexible. Putting the pronoun это before the verb (это купить) is a very natural conversational flow. Moving it to the end (купить это) is also correct but places slightly more emphasis on the word 'it'.
Why use the perfective verb купить here instead of the imperfective покупать?