How to purchase a gift certificate in iTunes store?
In many countries, you can easily do this from iTunes when signed in to a valid account with a credit card entered. I've never gifted to an account foreign to the US, so these steps are only proofed for the US store. 

On a computer:


open iTunes and connect the computer to the internet.
from the Store menu - select Home (Command-Shift-H on OS X)
scroll down a bit on the right hand side and click "Send iTunes Gifts"
fill out the gift form to email a gift


You can also send gifts from iOS iTunes Store:


open the App
tap any of the icons at the bottom (except Genius, Purchased or Downloads)
swipe the content up to see the bottom of the page
tap on Send Gift at the bottom right
fill out the gift form to email a gift




Fill out the form or at the bottom of the page is a link to a FAQ on gifting. It has links to the web store for gifting if you wish to check out in a web browser or from a computer without iTunes installed. Here is that link for the US store (but looking at it, it might be fragile and change from time to time):


http://store.apple.com/us/personalize/itunes?aid=AOS-US-iTunestile-GC&amp;product=ITUNES_GIFT_CARDS-101703


As you have discovered, the web store only sends physical gift cards for iTunes and physical gift cards for the Apple Stores (retail, online) and not certificates that can be emailed. Only iTunes will email certificates directly to your chosen recipients.