I took my initial Class 1 in March and the only two options were AMS and AeMC. NATS in Gatwick weren't offering initials back then either. I'm pretty sure I contacted them to confirm. I also called AMS to book an appointment and the lady on the phone said she would send me an e-mail with all the info but I never received it so I ended up going to AeMC in London. I had to wait about a month though as I think they only do them once a week and they only do 4 or 5 at a time. I would call up sooner rather than later so it doesn't delay any other timelines you have.
AM