tenin ni kiitara, sono iyahon ha ima zaiko ga nai node, toriyose ni naru to iwareta.

Here 聞いたら means when I asked or after I asked.

• 聞く = to ask / to inquire / to hear, depending on context
• 聞いた = past form
• 〜たら can mean if, but it also very often means when or after when talking about something that actually happened

So in this sentence, 店員に聞いたら is not hypothetical. It means the speaker really did ask the clerk, and then got the following response.

Because 店員 is the person the speaker asked.

With 聞く meaning to ask, the person you ask is commonly marked by に:

• 先生に聞く = ask the teacher
• 友だちに聞く = ask a friend

So:

• 店員に聞いたら = when I asked the store clerk

They are doing different jobs.

• そのイヤホンは sets the earphones as the main topic
• 在庫がない says what is true about the stock: there is no stock

So the structure is basically:

• As for those earphones, there is no stock right now

This is very common in Japanese:

• Topic marked by は
• The thing that exists / does not exist marked by が

So 在庫がない is natural because ない is describing the existence of stock.

今 here means now / at the moment / currently.

So 今在庫がない means:

• there is no stock right now
• it is currently out of stock

No particle is needed because 今 is acting like an adverb, modifying the whole statement.

Compare:

• 今行く = I’m going now
• 今忙しい = I’m busy now
• 今在庫がない = there’s no stock now

ので gives a reason: because / since.

Here:

• 在庫がないので = because it is out of stock

Compared with から, ので often sounds:

• a little softer
• a little more explanatory
• more common in polite or customer-service style speech

In a store context, ので sounds very natural because it gives a calm explanation.

取り寄せ means ordering something in from another location, such as a warehouse, another branch, or the manufacturer.

It is based on the verb 取り寄せる:

• 取り寄せる = to order in / to bring in from elsewhere

As a noun:

• 取り寄せ = special order / ordering in

So this is not just a generic order in the online-shopping sense. It specifically suggests the item is not currently in stock here and must be brought from somewhere else.

取り寄せになる is a very common business/store expression.

Literally, 〜になる means to become, but in this kind of context it often means:

• it will be handled as ...
• it will end up being ...
• it will have to be ...

So 取り寄せになる means something like:

• it will have to be specially ordered
• it will be an order-in item
• we’ll need to order it from elsewhere

This sounds more indirect and polite than a blunt statement like 取り寄せます.

The と marks the content of what was said.

So:

• 取り寄せになる = it will have to be ordered in
• 取り寄せになると言われた = I was told that it would have to be ordered in

This と is very common before verbs like:

• 言う = say
• 思う = think
• 聞く = hear

It works a lot like a quotation or content marker.

Because the speaker is focusing on receiving the information, not on the clerk as the active speaker.

• 言った = said
• 言われた = was told

So と言われた means:

• I was told that ...

This is very natural in Japanese when reporting what someone told you. The person doing the telling can be left unstated because it is obvious from context that it was the clerk.

Yes. The understood meaning is:

• the clerk said it
• I was told it

Japanese often leaves out things that are obvious from context. So even though the sentence does not explicitly say:

• 店員にそう言われた

that is what is understood.

A fuller version could be something like:

• 店員に聞いたら、そのイヤホンは今在庫がないので、取り寄せになると店員に言われた。

But that sounds repetitive, so the natural sentence omits what is already clear.

その refers to that earphone / those earphones near the listener’s side of the conversation, or more generally the earphones we’re talking about.

In natural English, it may simply be translated as:

• the earphones
• those earphones

Japanese uses:

• この = this
• その = that
• あの = that over there

Here その shows that the item had already been identified in the conversation.

It can be either, depending on context.

Japanese nouns usually do not change form for singular vs. plural. So イヤホン could mean:

• an earphone
• earphones
• a pair of earphones

In real usage, イヤホン often refers to earphones / earbuds as a product item, and the exact number is understood from the situation.

Yes. 聞く can mean several related things:

• hear
• listen
• ask

The core idea is connected to receiving information.

Examples:

• 音楽を聞く = listen to music
• 話を聞く = listen to a story / hear what someone says
• 先生に聞く = ask the teacher

In this sentence, because it is 店員に聞いたら, it clearly means asked the clerk.

Yes. It breaks down like this:

• 店員に聞いたら、
  when I asked the store clerk,

• そのイヤホンは今在庫がないので、
  those earphones are currently out of stock, so

• 取り寄せになると
  that it would have to be specially ordered

• 言われた。
  I was told.

This kind of chunking helps a lot with long Japanese sentences, especially when there is a quoted statement inside another statement.