Is it possible to get Zakum helm without the service?

Just get a Lord Pirate's Hat as an alternative.
Then fight zakum yourself once you're 135 or 140 (with a party ofc).

 

Why must the other players not have the helm?

The cheapest and easiest method is simply to have 3 to 5 higher level friends.

 

If you want to get you own on your own then being at least lvl 135 will be the way to go. You could even go lower level than that, but at 135 you get the exp.

Some times people in the community will take you in and give you a free helm. I've done it plenty of times, just gotta stay alive to grab one in the end if you don't need HB or anything.

Depending on your class, you'll just need hp gear.

 

If you're insistent on getting a helm with other players of the same level, you may be able to form a party and defeat Ravana at an earlier level than Zak in order to farm the Ravana Helms.

 

It’s recommended to get a Zak helm early as it’s relatively cheap for the boosts it provides. The stats are significant but the real value at level 50 is the weapon defense, as it’ll save you a ton in pots as you level. Zak is recommended for this as it’s lower level and higher Wdef than alternatives like Rav helm and Pirate hat.

That being said there’s no strict requirement to get one, it’s just recommended because it’s extremely effective for what you’re paying for.

 

if you go to pirate pq helmet you get it in around lv 65, and can do zak as attacker...

imo, better get a svc

 

Seems most players are missing the point of your question as they see the game purely from a mix/max perspective. Unfortunately, I think it would be tough to find a group of 13x helm-less players at this stage of the server. I'm assuming the earliest zakum runs in this server were players around level 13x-14x. They likely weren't very fast runs as they probably had worse gear and worse skillbooks(no tt NLs until zak dies) than the average 13x now as well, but it's very do-able with a 13x party. One option is you could wait til that level and host your own run and ask players if they want to roll for helms, but they will probably all have their own helms at that point and there isn't much you could do about that. Another option that may interest you is the "NewLeaf" guild but it would require you to start a new character.