Actually you can't get brown trout only tickets on the Deveron at any time it's always all species access.
Trouble with back end Deveron isn't you can't fish for browns, it's the cost, you're paying for a salmon ticket 'cause that's all you can get.
Being one of the last water's in the area to close (Spey having shut 30th Sept) it can also be quite popular so best to book ahead.
Frank Henderson at Turriff Tackle will keep you right and will certainly know what's available and how much.
Cheers
Allan L