Recently my shamisen fell and broken one of the tuning pegs , when asking the online shamisen store, they told me that I should bring the whole shamisen back to replace a new itomaki . I don’t fine this economically feasible as I don’t live in Japan and so should I just order it online instead?
Itomaki must be fitted to the zagane of each shamisen. You could buy blank itomaki online and fit them yourself, but there is a possibility of failure.
Is it worth the risk?
You have to make that judgement call for yourself, I’m afraid.
If you do not want to attempt it, you might see if @Kyle_Abbott could render services. He offers repair and has lovely itomaki
Thanks for the tag, @Brown!
Ouch, I’m so sorry that happened, @Riko! 
I wouldn’t exactly recommend buying an itomaki blank, as they are basically have a tapered hexagonal shape from end to end (I.e, one end isn’t pre-rounded), and so takes some skill to turn the end into a straight, tapered round peg with a file or lathe.
As Chris mentioned, I do have itomaki which I’ve made here in California. Most are very “boutique” level sets made with a variety of rosewoods and burls (https://bachido.com/product-category/parts-repair/itomaki/), but I do also have regular ebony itomaki available (Standard Ebony Itomaki Set – Bachido).
What’s more, they are pre-tapered so that the user is able to fit them to their shamisen. It still takes sandpaper (and a drill to make the string holes) to fit them, but the pre-shaping cuts hours off of the time.
Otherwise, if you were able to get blanks from the online shamisen store, I’d be happy to install those for you ($30/itomaki). I’m off to Berlin on Friday, and will be back in early May, and would be able to be of service then. 
Cheers!
Kyle
Depending on the shape of the break, that’s an easy repair. If you can extract the tip of the Itomaki, and post close up photos of the break, I can give you instructions on how to fix it.
But regardless of the repair, this Itomaki won’t have 100% structural integrity anymore, and I recommend the purchase of another set from Kyle.
However, fixing it will allow you to play while you wait for Kyle to get back.
Please let me know if you want the instructions.