to be honest the trout fishing is very tricky late on in the season. Best June through late August
Brown's or Tackle and Books in Tobermory will sort you for day tickets for a variety of lochs, Mishnish, Frisa, Tor
You may still be able to get a boat out of Ledmore or Lettermore on Frisa.
its a big old splash to be fishing from the bank
Rivers:
contact the Glenforsa estate for a ticket on the Forsa (caught my first Salmon there as a boy!)
The Lussa down deep south has good fish
and the Ba South of where you will be is short but can be productive
If it were me fishing this time of year:
Ballygowan bay (opposite the north end of Ulva)
Any where between the North West edge of Calgary bay (1/2 mile away from the beach) and the Caillach Point on the North West
both the same attack - off the rocks, spinners and/or shiney metal looking flies for Sea trout and Mackerel. You will catch coalfish and pollack as well by varying depth and lures.
personally I would take
Fish the high tide off Killiechronan away from the mouth of the Ba
and the same high tide on the opposite side of the "waist" of Mull opposite Aros Castle
best chance of a "sea borne" sea trout on the fly as the wait up at the mouths of the Ba and the Aros
Flies: Teal, Blue and Silver, Bloody Butchers, Black Spiders, Zulus, blues and reds
For the Sea Lures: Tobies and spoons over spinners and Mepps. Flying condoms
Flies for the sea: reservoir lures with plenty of flash and feather (think mackerel feathers you can cast!), poppers and bone fish style lures work too
good luck