I cant remember the name of the TA we used but if you do a search on FT they are there somewhere.

I communicated with them through emails on fares and seats availability. Tickets were delivered to my hotel when I arrived in Yangon, and I paid them in cash (USD). If I remember correctly payment could also be made by TT to their account (may not be possible from US) but I chose to pay with cash upon delivery of tickets.

Domestic tickets are not cheap in Burma, and its not worth doing Mandalay without Bagan. I would choose Bagan instead of Mandalay, I dont think there is another place on earth that is similar to Bagan and you will not be disappointed .