I've had mixed luck using American Express Platinum Travel. They've been waiving their fee since the pandemic. Sometimes agents there are excellent (although nowhere near as amazing as the travel agent I used to use for work trips). Some agents I just feed them the flight numbers, dates, inventory, cities, and boom, w're ready to go. Others insist on finding each flight through a painful process of searching. I asked an agent there about issuing xONEx tickets and she said it comes up as bookable no problem, and it gave her base fares that matches EF.