The ability to select different fare types only works on roundtrip tickets. For one-way tickets, there's no way to choose anything but whatever it gives you, or to select unrestricted which gives you a Y fare. This is one of the big deficiencies of the TG booking engine. If you want some other booking class, you'll have to purchase it via TG by phone or in person, or via a travel agent or perhaps an online travel site that shows you the booking class (most do not).

If you're flexible with the dates/times, then you can sometimes find another date or time where V is sold out and so it will automatically give you Q. In the past where I wanted to book online due to a major hassle of booking at their office, I booked a date that didn't have V, so was able to book in Q, then called up TG and changed it to the date I wanted. But that Q fare didn't have any penalties for changing. If there's a penalty, then that method isn't so good. And often the ticket is not valid before the original date of travel, so if you use that method you may have to purchase it for an original date prior to when you want to fly, then call up TG to change it to a later date.